Student Projects
We regularly offer Master and Bachelor theses in our group. This is an ideal chance if you want to enter
the field of Quantumoptics and Ultracold Quantumgases and learn more about these exciting fields. Within the framework
of a Semester thesis you can get first experiences in the everyday work inside our group. For about 6 weeks, you
have the opportunity to work on your own project. The semester work will be finished with a short report. Possible topics
are typically electronics development, optical setups, programming, vacuum technology and more. It is very helpful if you
already bring some experimental experience with you, which you for example can gain in the
Advanced Students Labs.
Applications are always welcome, please include a CV, your transcripts, and some lines of motivation.
The next round of projects will be decided on at the end of the current term, so ideally apply soon.
Do not hesitate to contact us and meet our group, we are looking forward to hearing from you!
Contact:
Tilman Esslinger and
Tobias Donner
Exemplary Open Projects
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
Past Projects
Software for automating optical alignment
Stephan Lempereur, February 2024
In his semester thesis, Stephen contributed to our ongoing efforts in automating optical alignment using prototypes of mirror mounts and motors characterized in a previous iteration of this project.
He developed software capable of sending control
commands to a microcontroller, which processes and forwards them via an Ethernet cable to the motors.
A Low-Noise Eight-Channel Arbitrary Waveform Generator for Quantum Gas Experiments
Shijia Chen, September 2023
For his master thesis, Shijia upgraded both the hardware and software of our custom and low-noise arbitrary waveform generated to allow for 8 independent output channel, all synchronized to the rest of the experiment by an external 10 MHz clock and digital trigger. With these upgrades, the device is at a “plug and play” level of flexibility and is ready for final tests in the lab.
Characterisation and Optimisation of a Custom AWG for Low-Noise and High-Precision Control of Quantum Gas Experiments
Kevin Mondoloni, August 2023
For his semester project, Kevin continued the work of Bahadir Dönmez on the development of a low-noise signal generator. Kevin performed extensive tests and simulations of the various digital and analog signals on both the power supply and DAC boards. He identified and replaced a number of components introducing noise in the output signal and tuned the filters at several stages in the signal chain to below 100 nV/sqrt(Hz) while maintaining the required bandwidth of 1 MHz for agile, arbitrary waveform generation.
Novel Offset Locking Scheme
Yu Liu, August 2023
Yu Liu programmed, set up, and tested a novel scheme to stabilize the relative frequency of two lasers in his semester project with the impact team, co-supervised by Kadir from the Quantum Engineering Center. His implementation utilizes a RedPitaya FPGA which is used to count the zero crossings of the beat note of two lasers. Yu developed an adaptive algorithm that allows for an accurate and high bandwidth determination of the laser offset frequency, outperforming standard FFT approaches with fixed integration window sizes. The setup further includes an electronic prescaler to extend the frequency range of the device. He demonstrated a perfectly linear frequency to voltage conversion, an important improvement compared to traditional offset locks. Offset frequencies up to 1.2 GHz and frequency resolutions down to 100 kHz have been demonstrated. The device is now a vital part of our experiment, and can also be used to analyze radio frequency sources in real time, or to read out the count rate of single photon counting modules.
The Quantumod: an RF Signal Generator for Quantum Gas Experiments
Chidzahi Mabritto and Ho June Kim, June 2023
During their project supervised jointly by the Lithium team and Gadgets lab, Chidzahi and Ho June developed the firmware for the high-performance microcontroller (MCU) on board a home-built radio frequency synthesizer based on direct digital synthesis (DDS). Using the hardware designed and built by the group's electrical engineer Alex Frank, Ho June implemented an Ethernet network interface based on the lwIP library between the MCU and a master PC, and Chidzahi developed the realtime control program to implement arbitrary sequences of setting and sweeping of the frequency, amplitude, and phase with precise and accurate timing.
Floquet Dynamics in Open Quantum Systems and the Non-Ideal Lambda System
Daniel Augusto Ortuño Gonzáles, May 2023
For his semester project with the Lithium team, Daniel developed and implemented an efficient algorithm to solve the time dynamics of open quantum systems subject to a periodic drive. This algorithm is based on the matrix representation of the system’s Liouville superoperator and Trotterization in time. By implementing this algorithm with a graphical processing unit to perform the bottleneck subroutines (diagonalisation of the Liouvillian), Daniel was able to achieve a speedup of a factor of 50 over the equivalent simulation in QuTiP. Using this code, Daniel performed simulations of the non-ideal lambda system found in Lithium6 at high magnetic fields recently explored in the experiment.
Towards a Distributed Low‐Noise Signal Generation System for Quantum Gas Experiments
Bahadir Dönmez, November 2022
During his master thesis supervised jointly by the Lithium team and Engineering Unit of the Quantum Center, Badir continued the development by Lukas and David Pahl of a low-noise analog signal generator to bring the system to its first functional prototype. As part of this process, he redesigned the system to split the PCBs into two stacked PCBs — one for the digital signal conversion and power regulation, and another hosting all the low-noise analog electronics. He also made several upgrades to both the programmable software and logic of the FPGA to improve timing flexibility and accuracy as well as overall performance.
A low-noise, high-speed and scalable FPGA-based analog signal generator for quantum gas experiments
Lukas Pahl, David Pahl, August 2022
David and Lukas designed and built a new analog signal generator based on a field-programmable gate array (FPGA) development
board, a custom PCB hosting a digital-to-analog converter (DAC) with 20-bit precision capable of 1 megasample per second (MSPS), and a custom breakout board. The FPGA development board accepts data from a master PC via TCP/IP where a user programs the waveform and dynamic sampling rate of each output channel and writes the data to onboard RAM. At runtime, the direct memory access (DMA) and Serial Peripheral Interface (SPI) modules inside the FPGA stream data to the custom DAC board via an Ethernet cable carrying the samples as differential signals along with the supply voltage. They designed the DAC board to be resistant to digital and analog noise by separating ground planes to prevent ground loops and by using high-precision and low-noise power supplies and voltage reference circuits. External trigger and clock inputs can be used to synchronize the DACs and multiple FPGAs. The time resolution and precision of their solution is optimized for experiments on quantum gases though it is flexible and can be adapted for many more applications.
A Control Algorithm for Acouso-Optic Modulators
Samuel Jele, Juli 2022
In this semester project, Samuel tested a new control algorithm specifically for the use of acousto-optic
modulators (AOMs) as the actuator in control loops. The go-to control algorithm used in these cases so
far is a standard PID controller. However, AOMs exhibit a so called dead-time: a delay between changes
on the RF-input and the resulting change in diffracted light, which is a consequence of the finite speed of
sound in the crystal material of the AOM. Such dead-time can limit the performance of a PID controller. To
improve the performance of the control loop, Samuel proposed the use of a Smith predictor, an algorithm
that makes use of a simplified model of the system to predict the system response to a control signal
without dead-time. For this, he found a first-order model of the AOM, implemented the Smith predictor
on the LockStar system and tested its performance against a standard PID controller.
Real-time Laser Beam Stabilization using an FPGA
Enis Mustafa, June 2022
Enis designed a versatile laser beam stabilization platform based on multiple CameraLink interfaced cameras to an FPGA. The system provides both real-time beam characterization and feedback on any possible beam parameter. For laser stabilization, low-latency, high-frame-rate profiling is required due to unpredictable disturbances such temperature changes and mechanical vibrations. This semester project implements a runtime tunable PID controller on an FPGA. Through DAC channels, four parallel PID modules supply feedback for the steering mirrors that stabilize the beam. Controlling the incidence angle of the laser beam onto the input plane is possible by using two cameras at different sample distances on the optical axis. The proposed system can be further enhanced with the implementation of machine learning based beam shape classification and also disturbance classification.
A closed loop, high-precision, high-speed Tip/Tilt Mirror
Jeremie Pilat, July 2022
In his semester thesis, Jeremie built and tested a Tip/Tilt mirror system. The complex transfer function of the mirror system was measured. No major mechanical resonances were seen up to 3kHz. The maximal displacement range of±4mrad of the mirror was both measured
and extrapolated with two different setups. Together they could measure both the dynamics and the
position of the diverted beam. The accuracy was estimated by measuring the linearisation and the
hysteresis of the Tip/Tilt mirror system. Locking the mirror with an PI-loop, implemented on the
Red Pitaya FPGA-board, lowered the hysteresis by a factor of 20 and the linearisation by a factor of
10. A noise audit was performed to estimate the 1/f noise and the noise spectrum of the individual
components of the system and the measurement setup. We showed that the PI-loop could remove
long term decay by locking the strain gauge and also improve 1/f noise by fixing the strain to the
unpowered value. A Python script was written to evaluate the measurements and the Pyrpl package
was used to implement the PI-loop for the FPGA-board.
Towards Automation of a Cold Atoms Experiment
Nathan Baudis, June 2022
In his semester thesis in the Cavity team, Nathan developed an automation framework to perform alignment procedures. He tackled two specific procedures: Firstly, the calibration procedure for correctly referencing the laser frequency to the cavity resonance was automated. Feedback on a frequency generator is obtained from a transmission measurement of the cavity. Secondly, the alignment of the upper transport beam, used to transport the atomic cloud into the cavity, was automated to optimally align the beam with the cavity mode. Here, absorption imaging of atoms trapped in the beam is performed, providing feedback for a motorized stage which moves a lens in the optical path. The procedures quickly and reliably perform the tasks at hand. He developed a GUI for easy control of these procedures, also paving the way for a more comprehensive automation of the experiment in the future.
Automatic Capacitance Meter (with Arduino ™)
Robin Weber, March 2022
Robin came to us to learn about electronics. He liked it so much that he stayed with us much longer than intended.
His final work (IPA, Individuelle praktische Arbeit) is an Arduino-based Automatic Capacitance Meter. Not only does it have Autorange capabilities,
but it can also be used in a complex measurement setup, as it speaks SCPI fluently via USB.
This Project was that successful, that it was presented at Swiss Skills 2022 in Berne.
Magnetic Field Stabilization System for the Lithium Experiment
Benjamin van Ommen, October 2021
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.
Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
Past Projects
Software for automating optical alignment
Stephan Lempereur, February 2024
In his semester thesis, Stephen contributed to our ongoing efforts in automating optical alignment using prototypes of mirror mounts and motors characterized in a previous iteration of this project.
He developed software capable of sending control
commands to a microcontroller, which processes and forwards them via an Ethernet cable to the motors.
A Low-Noise Eight-Channel Arbitrary Waveform Generator for Quantum Gas Experiments
Shijia Chen, September 2023
For his master thesis, Shijia upgraded both the hardware and software of our custom and low-noise arbitrary waveform generated to allow for 8 independent output channel, all synchronized to the rest of the experiment by an external 10 MHz clock and digital trigger. With these upgrades, the device is at a “plug and play” level of flexibility and is ready for final tests in the lab.
Characterisation and Optimisation of a Custom AWG for Low-Noise and High-Precision Control of Quantum Gas Experiments
Kevin Mondoloni, August 2023
For his semester project, Kevin continued the work of Bahadir Dönmez on the development of a low-noise signal generator. Kevin performed extensive tests and simulations of the various digital and analog signals on both the power supply and DAC boards. He identified and replaced a number of components introducing noise in the output signal and tuned the filters at several stages in the signal chain to below 100 nV/sqrt(Hz) while maintaining the required bandwidth of 1 MHz for agile, arbitrary waveform generation.
Novel Offset Locking Scheme
Yu Liu, August 2023
Yu Liu programmed, set up, and tested a novel scheme to stabilize the relative frequency of two lasers in his semester project with the impact team, co-supervised by Kadir from the Quantum Engineering Center. His implementation utilizes a RedPitaya FPGA which is used to count the zero crossings of the beat note of two lasers. Yu developed an adaptive algorithm that allows for an accurate and high bandwidth determination of the laser offset frequency, outperforming standard FFT approaches with fixed integration window sizes. The setup further includes an electronic prescaler to extend the frequency range of the device. He demonstrated a perfectly linear frequency to voltage conversion, an important improvement compared to traditional offset locks. Offset frequencies up to 1.2 GHz and frequency resolutions down to 100 kHz have been demonstrated. The device is now a vital part of our experiment, and can also be used to analyze radio frequency sources in real time, or to read out the count rate of single photon counting modules.
The Quantumod: an RF Signal Generator for Quantum Gas Experiments
Chidzahi Mabritto and Ho June Kim, June 2023
During their project supervised jointly by the Lithium team and Gadgets lab, Chidzahi and Ho June developed the firmware for the high-performance microcontroller (MCU) on board a home-built radio frequency synthesizer based on direct digital synthesis (DDS). Using the hardware designed and built by the group's electrical engineer Alex Frank, Ho June implemented an Ethernet network interface based on the lwIP library between the MCU and a master PC, and Chidzahi developed the realtime control program to implement arbitrary sequences of setting and sweeping of the frequency, amplitude, and phase with precise and accurate timing.
Floquet Dynamics in Open Quantum Systems and the Non-Ideal Lambda System
Daniel Augusto Ortuño Gonzáles, May 2023
For his semester project with the Lithium team, Daniel developed and implemented an efficient algorithm to solve the time dynamics of open quantum systems subject to a periodic drive. This algorithm is based on the matrix representation of the system’s Liouville superoperator and Trotterization in time. By implementing this algorithm with a graphical processing unit to perform the bottleneck subroutines (diagonalisation of the Liouvillian), Daniel was able to achieve a speedup of a factor of 50 over the equivalent simulation in QuTiP. Using this code, Daniel performed simulations of the non-ideal lambda system found in Lithium6 at high magnetic fields recently explored in the experiment.
Towards a Distributed Low‐Noise Signal Generation System for Quantum Gas Experiments
Bahadir Dönmez, November 2022
During his master thesis supervised jointly by the Lithium team and Engineering Unit of the Quantum Center, Badir continued the development by Lukas and David Pahl of a low-noise analog signal generator to bring the system to its first functional prototype. As part of this process, he redesigned the system to split the PCBs into two stacked PCBs — one for the digital signal conversion and power regulation, and another hosting all the low-noise analog electronics. He also made several upgrades to both the programmable software and logic of the FPGA to improve timing flexibility and accuracy as well as overall performance.
A low-noise, high-speed and scalable FPGA-based analog signal generator for quantum gas experiments
Lukas Pahl, David Pahl, August 2022
David and Lukas designed and built a new analog signal generator based on a field-programmable gate array (FPGA) development
board, a custom PCB hosting a digital-to-analog converter (DAC) with 20-bit precision capable of 1 megasample per second (MSPS), and a custom breakout board. The FPGA development board accepts data from a master PC via TCP/IP where a user programs the waveform and dynamic sampling rate of each output channel and writes the data to onboard RAM. At runtime, the direct memory access (DMA) and Serial Peripheral Interface (SPI) modules inside the FPGA stream data to the custom DAC board via an Ethernet cable carrying the samples as differential signals along with the supply voltage. They designed the DAC board to be resistant to digital and analog noise by separating ground planes to prevent ground loops and by using high-precision and low-noise power supplies and voltage reference circuits. External trigger and clock inputs can be used to synchronize the DACs and multiple FPGAs. The time resolution and precision of their solution is optimized for experiments on quantum gases though it is flexible and can be adapted for many more applications.
A Control Algorithm for Acouso-Optic Modulators
Samuel Jele, Juli 2022
In this semester project, Samuel tested a new control algorithm specifically for the use of acousto-optic
modulators (AOMs) as the actuator in control loops. The go-to control algorithm used in these cases so
far is a standard PID controller. However, AOMs exhibit a so called dead-time: a delay between changes
on the RF-input and the resulting change in diffracted light, which is a consequence of the finite speed of
sound in the crystal material of the AOM. Such dead-time can limit the performance of a PID controller. To
improve the performance of the control loop, Samuel proposed the use of a Smith predictor, an algorithm
that makes use of a simplified model of the system to predict the system response to a control signal
without dead-time. For this, he found a first-order model of the AOM, implemented the Smith predictor
on the LockStar system and tested its performance against a standard PID controller.
Real-time Laser Beam Stabilization using an FPGA
Enis Mustafa, June 2022
Enis designed a versatile laser beam stabilization platform based on multiple CameraLink interfaced cameras to an FPGA. The system provides both real-time beam characterization and feedback on any possible beam parameter. For laser stabilization, low-latency, high-frame-rate profiling is required due to unpredictable disturbances such temperature changes and mechanical vibrations. This semester project implements a runtime tunable PID controller on an FPGA. Through DAC channels, four parallel PID modules supply feedback for the steering mirrors that stabilize the beam. Controlling the incidence angle of the laser beam onto the input plane is possible by using two cameras at different sample distances on the optical axis. The proposed system can be further enhanced with the implementation of machine learning based beam shape classification and also disturbance classification.
A closed loop, high-precision, high-speed Tip/Tilt Mirror
Jeremie Pilat, July 2022
In his semester thesis, Jeremie built and tested a Tip/Tilt mirror system. The complex transfer function of the mirror system was measured. No major mechanical resonances were seen up to 3kHz. The maximal displacement range of±4mrad of the mirror was both measured
and extrapolated with two different setups. Together they could measure both the dynamics and the
position of the diverted beam. The accuracy was estimated by measuring the linearisation and the
hysteresis of the Tip/Tilt mirror system. Locking the mirror with an PI-loop, implemented on the
Red Pitaya FPGA-board, lowered the hysteresis by a factor of 20 and the linearisation by a factor of
10. A noise audit was performed to estimate the 1/f noise and the noise spectrum of the individual
components of the system and the measurement setup. We showed that the PI-loop could remove
long term decay by locking the strain gauge and also improve 1/f noise by fixing the strain to the
unpowered value. A Python script was written to evaluate the measurements and the Pyrpl package
was used to implement the PI-loop for the FPGA-board.
Towards Automation of a Cold Atoms Experiment
Nathan Baudis, June 2022
In his semester thesis in the Cavity team, Nathan developed an automation framework to perform alignment procedures. He tackled two specific procedures: Firstly, the calibration procedure for correctly referencing the laser frequency to the cavity resonance was automated. Feedback on a frequency generator is obtained from a transmission measurement of the cavity. Secondly, the alignment of the upper transport beam, used to transport the atomic cloud into the cavity, was automated to optimally align the beam with the cavity mode. Here, absorption imaging of atoms trapped in the beam is performed, providing feedback for a motorized stage which moves a lens in the optical path. The procedures quickly and reliably perform the tasks at hand. He developed a GUI for easy control of these procedures, also paving the way for a more comprehensive automation of the experiment in the future.
Automatic Capacitance Meter (with Arduino ™)
Robin Weber, March 2022
Robin came to us to learn about electronics. He liked it so much that he stayed with us much longer than intended.
His final work (IPA, Individuelle praktische Arbeit) is an Arduino-based Automatic Capacitance Meter. Not only does it have Autorange capabilities,
but it can also be used in a complex measurement setup, as it speaks SCPI fluently via USB.
This Project was that successful, that it was presented at Swiss Skills 2022 in Berne.
Magnetic Field Stabilization System for the Lithium Experiment
Benjamin van Ommen, October 2021
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.
Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
For his master thesis, Shijia upgraded both the hardware and software of our custom and low-noise arbitrary waveform generated to allow for 8 independent output channel, all synchronized to the rest of the experiment by an external 10 MHz clock and digital trigger. With these upgrades, the device is at a “plug and play” level of flexibility and is ready for final tests in the lab.
Characterisation and Optimisation of a Custom AWG for Low-Noise and High-Precision Control of Quantum Gas Experiments
Kevin Mondoloni, August 2023
For his semester project, Kevin continued the work of Bahadir Dönmez on the development of a low-noise signal generator. Kevin performed extensive tests and simulations of the various digital and analog signals on both the power supply and DAC boards. He identified and replaced a number of components introducing noise in the output signal and tuned the filters at several stages in the signal chain to below 100 nV/sqrt(Hz) while maintaining the required bandwidth of 1 MHz for agile, arbitrary waveform generation.
Novel Offset Locking Scheme
Yu Liu, August 2023
Yu Liu programmed, set up, and tested a novel scheme to stabilize the relative frequency of two lasers in his semester project with the impact team, co-supervised by Kadir from the Quantum Engineering Center. His implementation utilizes a RedPitaya FPGA which is used to count the zero crossings of the beat note of two lasers. Yu developed an adaptive algorithm that allows for an accurate and high bandwidth determination of the laser offset frequency, outperforming standard FFT approaches with fixed integration window sizes. The setup further includes an electronic prescaler to extend the frequency range of the device. He demonstrated a perfectly linear frequency to voltage conversion, an important improvement compared to traditional offset locks. Offset frequencies up to 1.2 GHz and frequency resolutions down to 100 kHz have been demonstrated. The device is now a vital part of our experiment, and can also be used to analyze radio frequency sources in real time, or to read out the count rate of single photon counting modules.
The Quantumod: an RF Signal Generator for Quantum Gas Experiments
Chidzahi Mabritto and Ho June Kim, June 2023
During their project supervised jointly by the Lithium team and Gadgets lab, Chidzahi and Ho June developed the firmware for the high-performance microcontroller (MCU) on board a home-built radio frequency synthesizer based on direct digital synthesis (DDS). Using the hardware designed and built by the group's electrical engineer Alex Frank, Ho June implemented an Ethernet network interface based on the lwIP library between the MCU and a master PC, and Chidzahi developed the realtime control program to implement arbitrary sequences of setting and sweeping of the frequency, amplitude, and phase with precise and accurate timing.
Floquet Dynamics in Open Quantum Systems and the Non-Ideal Lambda System
Daniel Augusto Ortuño Gonzáles, May 2023
For his semester project with the Lithium team, Daniel developed and implemented an efficient algorithm to solve the time dynamics of open quantum systems subject to a periodic drive. This algorithm is based on the matrix representation of the system’s Liouville superoperator and Trotterization in time. By implementing this algorithm with a graphical processing unit to perform the bottleneck subroutines (diagonalisation of the Liouvillian), Daniel was able to achieve a speedup of a factor of 50 over the equivalent simulation in QuTiP. Using this code, Daniel performed simulations of the non-ideal lambda system found in Lithium6 at high magnetic fields recently explored in the experiment.
Towards a Distributed Low‐Noise Signal Generation System for Quantum Gas Experiments
Bahadir Dönmez, November 2022
During his master thesis supervised jointly by the Lithium team and Engineering Unit of the Quantum Center, Badir continued the development by Lukas and David Pahl of a low-noise analog signal generator to bring the system to its first functional prototype. As part of this process, he redesigned the system to split the PCBs into two stacked PCBs — one for the digital signal conversion and power regulation, and another hosting all the low-noise analog electronics. He also made several upgrades to both the programmable software and logic of the FPGA to improve timing flexibility and accuracy as well as overall performance.
A low-noise, high-speed and scalable FPGA-based analog signal generator for quantum gas experiments
Lukas Pahl, David Pahl, August 2022
David and Lukas designed and built a new analog signal generator based on a field-programmable gate array (FPGA) development
board, a custom PCB hosting a digital-to-analog converter (DAC) with 20-bit precision capable of 1 megasample per second (MSPS), and a custom breakout board. The FPGA development board accepts data from a master PC via TCP/IP where a user programs the waveform and dynamic sampling rate of each output channel and writes the data to onboard RAM. At runtime, the direct memory access (DMA) and Serial Peripheral Interface (SPI) modules inside the FPGA stream data to the custom DAC board via an Ethernet cable carrying the samples as differential signals along with the supply voltage. They designed the DAC board to be resistant to digital and analog noise by separating ground planes to prevent ground loops and by using high-precision and low-noise power supplies and voltage reference circuits. External trigger and clock inputs can be used to synchronize the DACs and multiple FPGAs. The time resolution and precision of their solution is optimized for experiments on quantum gases though it is flexible and can be adapted for many more applications.
A Control Algorithm for Acouso-Optic Modulators
Samuel Jele, Juli 2022
In this semester project, Samuel tested a new control algorithm specifically for the use of acousto-optic
modulators (AOMs) as the actuator in control loops. The go-to control algorithm used in these cases so
far is a standard PID controller. However, AOMs exhibit a so called dead-time: a delay between changes
on the RF-input and the resulting change in diffracted light, which is a consequence of the finite speed of
sound in the crystal material of the AOM. Such dead-time can limit the performance of a PID controller. To
improve the performance of the control loop, Samuel proposed the use of a Smith predictor, an algorithm
that makes use of a simplified model of the system to predict the system response to a control signal
without dead-time. For this, he found a first-order model of the AOM, implemented the Smith predictor
on the LockStar system and tested its performance against a standard PID controller.
Real-time Laser Beam Stabilization using an FPGA
Enis Mustafa, June 2022
Enis designed a versatile laser beam stabilization platform based on multiple CameraLink interfaced cameras to an FPGA. The system provides both real-time beam characterization and feedback on any possible beam parameter. For laser stabilization, low-latency, high-frame-rate profiling is required due to unpredictable disturbances such temperature changes and mechanical vibrations. This semester project implements a runtime tunable PID controller on an FPGA. Through DAC channels, four parallel PID modules supply feedback for the steering mirrors that stabilize the beam. Controlling the incidence angle of the laser beam onto the input plane is possible by using two cameras at different sample distances on the optical axis. The proposed system can be further enhanced with the implementation of machine learning based beam shape classification and also disturbance classification.
A closed loop, high-precision, high-speed Tip/Tilt Mirror
Jeremie Pilat, July 2022
In his semester thesis, Jeremie built and tested a Tip/Tilt mirror system. The complex transfer function of the mirror system was measured. No major mechanical resonances were seen up to 3kHz. The maximal displacement range of±4mrad of the mirror was both measured
and extrapolated with two different setups. Together they could measure both the dynamics and the
position of the diverted beam. The accuracy was estimated by measuring the linearisation and the
hysteresis of the Tip/Tilt mirror system. Locking the mirror with an PI-loop, implemented on the
Red Pitaya FPGA-board, lowered the hysteresis by a factor of 20 and the linearisation by a factor of
10. A noise audit was performed to estimate the 1/f noise and the noise spectrum of the individual
components of the system and the measurement setup. We showed that the PI-loop could remove
long term decay by locking the strain gauge and also improve 1/f noise by fixing the strain to the
unpowered value. A Python script was written to evaluate the measurements and the Pyrpl package
was used to implement the PI-loop for the FPGA-board.
Towards Automation of a Cold Atoms Experiment
Nathan Baudis, June 2022
In his semester thesis in the Cavity team, Nathan developed an automation framework to perform alignment procedures. He tackled two specific procedures: Firstly, the calibration procedure for correctly referencing the laser frequency to the cavity resonance was automated. Feedback on a frequency generator is obtained from a transmission measurement of the cavity. Secondly, the alignment of the upper transport beam, used to transport the atomic cloud into the cavity, was automated to optimally align the beam with the cavity mode. Here, absorption imaging of atoms trapped in the beam is performed, providing feedback for a motorized stage which moves a lens in the optical path. The procedures quickly and reliably perform the tasks at hand. He developed a GUI for easy control of these procedures, also paving the way for a more comprehensive automation of the experiment in the future.
Automatic Capacitance Meter (with Arduino ™)
Robin Weber, March 2022
Robin came to us to learn about electronics. He liked it so much that he stayed with us much longer than intended.
His final work (IPA, Individuelle praktische Arbeit) is an Arduino-based Automatic Capacitance Meter. Not only does it have Autorange capabilities,
but it can also be used in a complex measurement setup, as it speaks SCPI fluently via USB.
This Project was that successful, that it was presented at Swiss Skills 2022 in Berne.
Magnetic Field Stabilization System for the Lithium Experiment
Benjamin van Ommen, October 2021
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.
Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
Yu Liu programmed, set up, and tested a novel scheme to stabilize the relative frequency of two lasers in his semester project with the impact team, co-supervised by Kadir from the Quantum Engineering Center. His implementation utilizes a RedPitaya FPGA which is used to count the zero crossings of the beat note of two lasers. Yu developed an adaptive algorithm that allows for an accurate and high bandwidth determination of the laser offset frequency, outperforming standard FFT approaches with fixed integration window sizes. The setup further includes an electronic prescaler to extend the frequency range of the device. He demonstrated a perfectly linear frequency to voltage conversion, an important improvement compared to traditional offset locks. Offset frequencies up to 1.2 GHz and frequency resolutions down to 100 kHz have been demonstrated. The device is now a vital part of our experiment, and can also be used to analyze radio frequency sources in real time, or to read out the count rate of single photon counting modules.
The Quantumod: an RF Signal Generator for Quantum Gas Experiments
Chidzahi Mabritto and Ho June Kim, June 2023
During their project supervised jointly by the Lithium team and Gadgets lab, Chidzahi and Ho June developed the firmware for the high-performance microcontroller (MCU) on board a home-built radio frequency synthesizer based on direct digital synthesis (DDS). Using the hardware designed and built by the group's electrical engineer Alex Frank, Ho June implemented an Ethernet network interface based on the lwIP library between the MCU and a master PC, and Chidzahi developed the realtime control program to implement arbitrary sequences of setting and sweeping of the frequency, amplitude, and phase with precise and accurate timing.
Floquet Dynamics in Open Quantum Systems and the Non-Ideal Lambda System
Daniel Augusto Ortuño Gonzáles, May 2023
For his semester project with the Lithium team, Daniel developed and implemented an efficient algorithm to solve the time dynamics of open quantum systems subject to a periodic drive. This algorithm is based on the matrix representation of the system’s Liouville superoperator and Trotterization in time. By implementing this algorithm with a graphical processing unit to perform the bottleneck subroutines (diagonalisation of the Liouvillian), Daniel was able to achieve a speedup of a factor of 50 over the equivalent simulation in QuTiP. Using this code, Daniel performed simulations of the non-ideal lambda system found in Lithium6 at high magnetic fields recently explored in the experiment.
Towards a Distributed Low‐Noise Signal Generation System for Quantum Gas Experiments
Bahadir Dönmez, November 2022
During his master thesis supervised jointly by the Lithium team and Engineering Unit of the Quantum Center, Badir continued the development by Lukas and David Pahl of a low-noise analog signal generator to bring the system to its first functional prototype. As part of this process, he redesigned the system to split the PCBs into two stacked PCBs — one for the digital signal conversion and power regulation, and another hosting all the low-noise analog electronics. He also made several upgrades to both the programmable software and logic of the FPGA to improve timing flexibility and accuracy as well as overall performance.
A low-noise, high-speed and scalable FPGA-based analog signal generator for quantum gas experiments
Lukas Pahl, David Pahl, August 2022
David and Lukas designed and built a new analog signal generator based on a field-programmable gate array (FPGA) development
board, a custom PCB hosting a digital-to-analog converter (DAC) with 20-bit precision capable of 1 megasample per second (MSPS), and a custom breakout board. The FPGA development board accepts data from a master PC via TCP/IP where a user programs the waveform and dynamic sampling rate of each output channel and writes the data to onboard RAM. At runtime, the direct memory access (DMA) and Serial Peripheral Interface (SPI) modules inside the FPGA stream data to the custom DAC board via an Ethernet cable carrying the samples as differential signals along with the supply voltage. They designed the DAC board to be resistant to digital and analog noise by separating ground planes to prevent ground loops and by using high-precision and low-noise power supplies and voltage reference circuits. External trigger and clock inputs can be used to synchronize the DACs and multiple FPGAs. The time resolution and precision of their solution is optimized for experiments on quantum gases though it is flexible and can be adapted for many more applications.
A Control Algorithm for Acouso-Optic Modulators
Samuel Jele, Juli 2022
In this semester project, Samuel tested a new control algorithm specifically for the use of acousto-optic
modulators (AOMs) as the actuator in control loops. The go-to control algorithm used in these cases so
far is a standard PID controller. However, AOMs exhibit a so called dead-time: a delay between changes
on the RF-input and the resulting change in diffracted light, which is a consequence of the finite speed of
sound in the crystal material of the AOM. Such dead-time can limit the performance of a PID controller. To
improve the performance of the control loop, Samuel proposed the use of a Smith predictor, an algorithm
that makes use of a simplified model of the system to predict the system response to a control signal
without dead-time. For this, he found a first-order model of the AOM, implemented the Smith predictor
on the LockStar system and tested its performance against a standard PID controller.
Real-time Laser Beam Stabilization using an FPGA
Enis Mustafa, June 2022
Enis designed a versatile laser beam stabilization platform based on multiple CameraLink interfaced cameras to an FPGA. The system provides both real-time beam characterization and feedback on any possible beam parameter. For laser stabilization, low-latency, high-frame-rate profiling is required due to unpredictable disturbances such temperature changes and mechanical vibrations. This semester project implements a runtime tunable PID controller on an FPGA. Through DAC channels, four parallel PID modules supply feedback for the steering mirrors that stabilize the beam. Controlling the incidence angle of the laser beam onto the input plane is possible by using two cameras at different sample distances on the optical axis. The proposed system can be further enhanced with the implementation of machine learning based beam shape classification and also disturbance classification.
A closed loop, high-precision, high-speed Tip/Tilt Mirror
Jeremie Pilat, July 2022
In his semester thesis, Jeremie built and tested a Tip/Tilt mirror system. The complex transfer function of the mirror system was measured. No major mechanical resonances were seen up to 3kHz. The maximal displacement range of±4mrad of the mirror was both measured
and extrapolated with two different setups. Together they could measure both the dynamics and the
position of the diverted beam. The accuracy was estimated by measuring the linearisation and the
hysteresis of the Tip/Tilt mirror system. Locking the mirror with an PI-loop, implemented on the
Red Pitaya FPGA-board, lowered the hysteresis by a factor of 20 and the linearisation by a factor of
10. A noise audit was performed to estimate the 1/f noise and the noise spectrum of the individual
components of the system and the measurement setup. We showed that the PI-loop could remove
long term decay by locking the strain gauge and also improve 1/f noise by fixing the strain to the
unpowered value. A Python script was written to evaluate the measurements and the Pyrpl package
was used to implement the PI-loop for the FPGA-board.
Towards Automation of a Cold Atoms Experiment
Nathan Baudis, June 2022
In his semester thesis in the Cavity team, Nathan developed an automation framework to perform alignment procedures. He tackled two specific procedures: Firstly, the calibration procedure for correctly referencing the laser frequency to the cavity resonance was automated. Feedback on a frequency generator is obtained from a transmission measurement of the cavity. Secondly, the alignment of the upper transport beam, used to transport the atomic cloud into the cavity, was automated to optimally align the beam with the cavity mode. Here, absorption imaging of atoms trapped in the beam is performed, providing feedback for a motorized stage which moves a lens in the optical path. The procedures quickly and reliably perform the tasks at hand. He developed a GUI for easy control of these procedures, also paving the way for a more comprehensive automation of the experiment in the future.
Automatic Capacitance Meter (with Arduino ™)
Robin Weber, March 2022
Robin came to us to learn about electronics. He liked it so much that he stayed with us much longer than intended.
His final work (IPA, Individuelle praktische Arbeit) is an Arduino-based Automatic Capacitance Meter. Not only does it have Autorange capabilities,
but it can also be used in a complex measurement setup, as it speaks SCPI fluently via USB.
This Project was that successful, that it was presented at Swiss Skills 2022 in Berne.
Magnetic Field Stabilization System for the Lithium Experiment
Benjamin van Ommen, October 2021
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.
Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
For his semester project with the Lithium team, Daniel developed and implemented an efficient algorithm to solve the time dynamics of open quantum systems subject to a periodic drive. This algorithm is based on the matrix representation of the system’s Liouville superoperator and Trotterization in time. By implementing this algorithm with a graphical processing unit to perform the bottleneck subroutines (diagonalisation of the Liouvillian), Daniel was able to achieve a speedup of a factor of 50 over the equivalent simulation in QuTiP. Using this code, Daniel performed simulations of the non-ideal lambda system found in Lithium6 at high magnetic fields recently explored in the experiment.
Towards a Distributed Low‐Noise Signal Generation System for Quantum Gas Experiments
Bahadir Dönmez, November 2022
During his master thesis supervised jointly by the Lithium team and Engineering Unit of the Quantum Center, Badir continued the development by Lukas and David Pahl of a low-noise analog signal generator to bring the system to its first functional prototype. As part of this process, he redesigned the system to split the PCBs into two stacked PCBs — one for the digital signal conversion and power regulation, and another hosting all the low-noise analog electronics. He also made several upgrades to both the programmable software and logic of the FPGA to improve timing flexibility and accuracy as well as overall performance.
A low-noise, high-speed and scalable FPGA-based analog signal generator for quantum gas experiments
Lukas Pahl, David Pahl, August 2022
David and Lukas designed and built a new analog signal generator based on a field-programmable gate array (FPGA) development
board, a custom PCB hosting a digital-to-analog converter (DAC) with 20-bit precision capable of 1 megasample per second (MSPS), and a custom breakout board. The FPGA development board accepts data from a master PC via TCP/IP where a user programs the waveform and dynamic sampling rate of each output channel and writes the data to onboard RAM. At runtime, the direct memory access (DMA) and Serial Peripheral Interface (SPI) modules inside the FPGA stream data to the custom DAC board via an Ethernet cable carrying the samples as differential signals along with the supply voltage. They designed the DAC board to be resistant to digital and analog noise by separating ground planes to prevent ground loops and by using high-precision and low-noise power supplies and voltage reference circuits. External trigger and clock inputs can be used to synchronize the DACs and multiple FPGAs. The time resolution and precision of their solution is optimized for experiments on quantum gases though it is flexible and can be adapted for many more applications.
A Control Algorithm for Acouso-Optic Modulators
Samuel Jele, Juli 2022
In this semester project, Samuel tested a new control algorithm specifically for the use of acousto-optic
modulators (AOMs) as the actuator in control loops. The go-to control algorithm used in these cases so
far is a standard PID controller. However, AOMs exhibit a so called dead-time: a delay between changes
on the RF-input and the resulting change in diffracted light, which is a consequence of the finite speed of
sound in the crystal material of the AOM. Such dead-time can limit the performance of a PID controller. To
improve the performance of the control loop, Samuel proposed the use of a Smith predictor, an algorithm
that makes use of a simplified model of the system to predict the system response to a control signal
without dead-time. For this, he found a first-order model of the AOM, implemented the Smith predictor
on the LockStar system and tested its performance against a standard PID controller.
Real-time Laser Beam Stabilization using an FPGA
Enis Mustafa, June 2022
Enis designed a versatile laser beam stabilization platform based on multiple CameraLink interfaced cameras to an FPGA. The system provides both real-time beam characterization and feedback on any possible beam parameter. For laser stabilization, low-latency, high-frame-rate profiling is required due to unpredictable disturbances such temperature changes and mechanical vibrations. This semester project implements a runtime tunable PID controller on an FPGA. Through DAC channels, four parallel PID modules supply feedback for the steering mirrors that stabilize the beam. Controlling the incidence angle of the laser beam onto the input plane is possible by using two cameras at different sample distances on the optical axis. The proposed system can be further enhanced with the implementation of machine learning based beam shape classification and also disturbance classification.
A closed loop, high-precision, high-speed Tip/Tilt Mirror
Jeremie Pilat, July 2022
In his semester thesis, Jeremie built and tested a Tip/Tilt mirror system. The complex transfer function of the mirror system was measured. No major mechanical resonances were seen up to 3kHz. The maximal displacement range of±4mrad of the mirror was both measured
and extrapolated with two different setups. Together they could measure both the dynamics and the
position of the diverted beam. The accuracy was estimated by measuring the linearisation and the
hysteresis of the Tip/Tilt mirror system. Locking the mirror with an PI-loop, implemented on the
Red Pitaya FPGA-board, lowered the hysteresis by a factor of 20 and the linearisation by a factor of
10. A noise audit was performed to estimate the 1/f noise and the noise spectrum of the individual
components of the system and the measurement setup. We showed that the PI-loop could remove
long term decay by locking the strain gauge and also improve 1/f noise by fixing the strain to the
unpowered value. A Python script was written to evaluate the measurements and the Pyrpl package
was used to implement the PI-loop for the FPGA-board.
Towards Automation of a Cold Atoms Experiment
Nathan Baudis, June 2022
In his semester thesis in the Cavity team, Nathan developed an automation framework to perform alignment procedures. He tackled two specific procedures: Firstly, the calibration procedure for correctly referencing the laser frequency to the cavity resonance was automated. Feedback on a frequency generator is obtained from a transmission measurement of the cavity. Secondly, the alignment of the upper transport beam, used to transport the atomic cloud into the cavity, was automated to optimally align the beam with the cavity mode. Here, absorption imaging of atoms trapped in the beam is performed, providing feedback for a motorized stage which moves a lens in the optical path. The procedures quickly and reliably perform the tasks at hand. He developed a GUI for easy control of these procedures, also paving the way for a more comprehensive automation of the experiment in the future.
Automatic Capacitance Meter (with Arduino ™)
Robin Weber, March 2022
Robin came to us to learn about electronics. He liked it so much that he stayed with us much longer than intended.
His final work (IPA, Individuelle praktische Arbeit) is an Arduino-based Automatic Capacitance Meter. Not only does it have Autorange capabilities,
but it can also be used in a complex measurement setup, as it speaks SCPI fluently via USB.
This Project was that successful, that it was presented at Swiss Skills 2022 in Berne.
Magnetic Field Stabilization System for the Lithium Experiment
Benjamin van Ommen, October 2021
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.
Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
David and Lukas designed and built a new analog signal generator based on a field-programmable gate array (FPGA) development
board, a custom PCB hosting a digital-to-analog converter (DAC) with 20-bit precision capable of 1 megasample per second (MSPS), and a custom breakout board. The FPGA development board accepts data from a master PC via TCP/IP where a user programs the waveform and dynamic sampling rate of each output channel and writes the data to onboard RAM. At runtime, the direct memory access (DMA) and Serial Peripheral Interface (SPI) modules inside the FPGA stream data to the custom DAC board via an Ethernet cable carrying the samples as differential signals along with the supply voltage. They designed the DAC board to be resistant to digital and analog noise by separating ground planes to prevent ground loops and by using high-precision and low-noise power supplies and voltage reference circuits. External trigger and clock inputs can be used to synchronize the DACs and multiple FPGAs. The time resolution and precision of their solution is optimized for experiments on quantum gases though it is flexible and can be adapted for many more applications.
A Control Algorithm for Acouso-Optic Modulators
Samuel Jele, Juli 2022
In this semester project, Samuel tested a new control algorithm specifically for the use of acousto-optic
modulators (AOMs) as the actuator in control loops. The go-to control algorithm used in these cases so
far is a standard PID controller. However, AOMs exhibit a so called dead-time: a delay between changes
on the RF-input and the resulting change in diffracted light, which is a consequence of the finite speed of
sound in the crystal material of the AOM. Such dead-time can limit the performance of a PID controller. To
improve the performance of the control loop, Samuel proposed the use of a Smith predictor, an algorithm
that makes use of a simplified model of the system to predict the system response to a control signal
without dead-time. For this, he found a first-order model of the AOM, implemented the Smith predictor
on the LockStar system and tested its performance against a standard PID controller.
Real-time Laser Beam Stabilization using an FPGA
Enis Mustafa, June 2022
Enis designed a versatile laser beam stabilization platform based on multiple CameraLink interfaced cameras to an FPGA. The system provides both real-time beam characterization and feedback on any possible beam parameter. For laser stabilization, low-latency, high-frame-rate profiling is required due to unpredictable disturbances such temperature changes and mechanical vibrations. This semester project implements a runtime tunable PID controller on an FPGA. Through DAC channels, four parallel PID modules supply feedback for the steering mirrors that stabilize the beam. Controlling the incidence angle of the laser beam onto the input plane is possible by using two cameras at different sample distances on the optical axis. The proposed system can be further enhanced with the implementation of machine learning based beam shape classification and also disturbance classification.
A closed loop, high-precision, high-speed Tip/Tilt Mirror
Jeremie Pilat, July 2022
In his semester thesis, Jeremie built and tested a Tip/Tilt mirror system. The complex transfer function of the mirror system was measured. No major mechanical resonances were seen up to 3kHz. The maximal displacement range of±4mrad of the mirror was both measured
and extrapolated with two different setups. Together they could measure both the dynamics and the
position of the diverted beam. The accuracy was estimated by measuring the linearisation and the
hysteresis of the Tip/Tilt mirror system. Locking the mirror with an PI-loop, implemented on the
Red Pitaya FPGA-board, lowered the hysteresis by a factor of 20 and the linearisation by a factor of
10. A noise audit was performed to estimate the 1/f noise and the noise spectrum of the individual
components of the system and the measurement setup. We showed that the PI-loop could remove
long term decay by locking the strain gauge and also improve 1/f noise by fixing the strain to the
unpowered value. A Python script was written to evaluate the measurements and the Pyrpl package
was used to implement the PI-loop for the FPGA-board.
Towards Automation of a Cold Atoms Experiment
Nathan Baudis, June 2022
In his semester thesis in the Cavity team, Nathan developed an automation framework to perform alignment procedures. He tackled two specific procedures: Firstly, the calibration procedure for correctly referencing the laser frequency to the cavity resonance was automated. Feedback on a frequency generator is obtained from a transmission measurement of the cavity. Secondly, the alignment of the upper transport beam, used to transport the atomic cloud into the cavity, was automated to optimally align the beam with the cavity mode. Here, absorption imaging of atoms trapped in the beam is performed, providing feedback for a motorized stage which moves a lens in the optical path. The procedures quickly and reliably perform the tasks at hand. He developed a GUI for easy control of these procedures, also paving the way for a more comprehensive automation of the experiment in the future.
Automatic Capacitance Meter (with Arduino ™)
Robin Weber, March 2022
Robin came to us to learn about electronics. He liked it so much that he stayed with us much longer than intended.
His final work (IPA, Individuelle praktische Arbeit) is an Arduino-based Automatic Capacitance Meter. Not only does it have Autorange capabilities,
but it can also be used in a complex measurement setup, as it speaks SCPI fluently via USB.
This Project was that successful, that it was presented at Swiss Skills 2022 in Berne.
Magnetic Field Stabilization System for the Lithium Experiment
Benjamin van Ommen, October 2021
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.
Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
Enis designed a versatile laser beam stabilization platform based on multiple CameraLink interfaced cameras to an FPGA. The system provides both real-time beam characterization and feedback on any possible beam parameter. For laser stabilization, low-latency, high-frame-rate profiling is required due to unpredictable disturbances such temperature changes and mechanical vibrations. This semester project implements a runtime tunable PID controller on an FPGA. Through DAC channels, four parallel PID modules supply feedback for the steering mirrors that stabilize the beam. Controlling the incidence angle of the laser beam onto the input plane is possible by using two cameras at different sample distances on the optical axis. The proposed system can be further enhanced with the implementation of machine learning based beam shape classification and also disturbance classification.
A closed loop, high-precision, high-speed Tip/Tilt Mirror
Jeremie Pilat, July 2022
In his semester thesis, Jeremie built and tested a Tip/Tilt mirror system. The complex transfer function of the mirror system was measured. No major mechanical resonances were seen up to 3kHz. The maximal displacement range of±4mrad of the mirror was both measured
and extrapolated with two different setups. Together they could measure both the dynamics and the
position of the diverted beam. The accuracy was estimated by measuring the linearisation and the
hysteresis of the Tip/Tilt mirror system. Locking the mirror with an PI-loop, implemented on the
Red Pitaya FPGA-board, lowered the hysteresis by a factor of 20 and the linearisation by a factor of
10. A noise audit was performed to estimate the 1/f noise and the noise spectrum of the individual
components of the system and the measurement setup. We showed that the PI-loop could remove
long term decay by locking the strain gauge and also improve 1/f noise by fixing the strain to the
unpowered value. A Python script was written to evaluate the measurements and the Pyrpl package
was used to implement the PI-loop for the FPGA-board.
Towards Automation of a Cold Atoms Experiment
Nathan Baudis, June 2022
In his semester thesis in the Cavity team, Nathan developed an automation framework to perform alignment procedures. He tackled two specific procedures: Firstly, the calibration procedure for correctly referencing the laser frequency to the cavity resonance was automated. Feedback on a frequency generator is obtained from a transmission measurement of the cavity. Secondly, the alignment of the upper transport beam, used to transport the atomic cloud into the cavity, was automated to optimally align the beam with the cavity mode. Here, absorption imaging of atoms trapped in the beam is performed, providing feedback for a motorized stage which moves a lens in the optical path. The procedures quickly and reliably perform the tasks at hand. He developed a GUI for easy control of these procedures, also paving the way for a more comprehensive automation of the experiment in the future.
Automatic Capacitance Meter (with Arduino ™)
Robin Weber, March 2022
Robin came to us to learn about electronics. He liked it so much that he stayed with us much longer than intended.
His final work (IPA, Individuelle praktische Arbeit) is an Arduino-based Automatic Capacitance Meter. Not only does it have Autorange capabilities,
but it can also be used in a complex measurement setup, as it speaks SCPI fluently via USB.
This Project was that successful, that it was presented at Swiss Skills 2022 in Berne.
Magnetic Field Stabilization System for the Lithium Experiment
Benjamin van Ommen, October 2021
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.
Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
In his semester thesis in the Cavity team, Nathan developed an automation framework to perform alignment procedures. He tackled two specific procedures: Firstly, the calibration procedure for correctly referencing the laser frequency to the cavity resonance was automated. Feedback on a frequency generator is obtained from a transmission measurement of the cavity. Secondly, the alignment of the upper transport beam, used to transport the atomic cloud into the cavity, was automated to optimally align the beam with the cavity mode. Here, absorption imaging of atoms trapped in the beam is performed, providing feedback for a motorized stage which moves a lens in the optical path. The procedures quickly and reliably perform the tasks at hand. He developed a GUI for easy control of these procedures, also paving the way for a more comprehensive automation of the experiment in the future.Automatic Capacitance Meter (with Arduino ™)
Robin Weber, March 2022
Robin came to us to learn about electronics. He liked it so much that he stayed with us much longer than intended.
His final work (IPA, Individuelle praktische Arbeit) is an Arduino-based Automatic Capacitance Meter. Not only does it have Autorange capabilities,
but it can also be used in a complex measurement setup, as it speaks SCPI fluently via USB.
This Project was that successful, that it was presented at Swiss Skills 2022 in Berne.
Magnetic Field Stabilization System for the Lithium Experiment
Benjamin van Ommen, October 2021
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.
Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
Benjamin investigated theoretically the influence of a noisy magnetic field on simulated experimental results and build a new magnetic field stabilization system. The magnetic field is noisy due to fluctuations in the current through the coils that generate the field, and due to ambient noise from devices in the lab. The existing system used feedback to stabilize the current going through the coils down to an rms noise of 10 ppm. The new system uses feedback to stabilize the current, but also uses feedforward to compensate for the ambient 50 Hz magnetic field. The new system was tested on a mock-up of the main experiment, where the current through the coils was stabilized to 0.96 ppm rms noise (48 μA rms at 50 A) using the feedback.Generating tunable optical lattices with a DMD
Franco Rabec, April 2021
In his master thesis in the Impact team, Franco investigated the generation of optical lattices using a
Digital Micromirror Device for Bragg spectroscopy applications. He
implemented a phase correction algorithm that flattens the strongly aberrated initial wavefront, allowing the projection of optical lattices
with much higher quality. The lattices are imaged in a test setup, where he measured the generation of optical lattices with tunable periods down to 650 nm whose orientation can be rotated
at arbitrary angles. He also demonstrated the generation of a 530 nm lattice at a fixed orientation and he managed to project lattices with several time-dependent phase profiles (linear, sinusoidal)
Phase & Amplitude-Locking of Two Counter-Propagating Laser Beams
Marius Gächter, February 2021
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.
Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
In his semester thesis in the cavity team, Marius investigated different strategies to implement a phase lock of two counter-propagating laser beams in a cheap, elegant and scalable way. In a dedicated test setup, he explored frequency modulation of a VCO, changing the optical path length via a piezo-actuated mirror, and electronically tuning the light phase through a phase shifter. While the frequency modulation solution proved cumbersome, piezo mirror and phas e shifter showed stable locking for tens of seconds with a bandwidth of 2 kHz. The phase shifter has the advantage of being readily daisy-chained, thus extending the available phase shift and enabling even longer locking times. Finally, combining the phase shifter with an on-board amplified RedPitaya to easily control and program PI loops gave a nice and useful addition to the QO gadgets.Towards a uniform two-dimensional channel for transport experiments with ultracold gases
Moritz Fontboté Schmidt, January 2021
Moritz joined the Lithium team for his semester thesis to work on evaluating the best way to generate a uniform 2D confinement potential for our transport experiment. A test setup for a liquid crystal on silicon spatial light modulator (LCoS-SLM) was put in place to evaluate pixel cross-talk, temporal phase noise and general applicability to our setup. The requirements were found to be met, however the price and complexity of setup asked for evaluating an alternative, custom-made glass phase plates. These were theoretically evaluated and found to meet our needs.
High transmission optical cleaning cavity
Benjamin van Ommen, January 2021
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
An agile precision digital-to-analog converter board for quantum optics experiments
Zhenning Liu, December 2020
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
Two color driving scheme of the Fermi Hubbard model and optical levitation with 532 nm light
Manish Sajnani, November 2020
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
High power 671 nm laser
Franco Rabec, October 2020
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Fast Digital Notch Filter
Philip Leindecker, September 2020
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Floquet bandstructure in 2D hexagonal lattices
Alex Gómez, September 2020
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
Single particle dynamics on an optical lattice
Manish Sajnani, April 2020
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Portable Gain / Phase Analyser - "Gainboy"
Patrick Helbingk, 19th of March 2020
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Frequency and Intensity Stabilization of Two Near-Commensurate Lasers
Sandra Buob, April 2019
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Automatic laser-fibre alignment
Felix Gast, 30 August 2018
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
Reducing noise in thermodynamic measurements
on interacting Fermi gases
Jeff Mohan, 19 September 2018
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
Laser Watchdog
Hinrich Mattiat, 16 April 2018
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Arduino / Genuino Spectrum Analyser
Mirco Dill, 10 March 2018
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Arbitrary 2D optical potentials with a digital micromirror device
Jeff Mohan, 13 December 2017
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Automated fiber coupling
13 September 2017
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Towards spin-dependent optical potentials
12 April 2017
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
Towards a high resolution imaging system for ultra cold atoms in two crossed cavities
29 March 2017
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Construction of a transfer cavity
30 June 2016
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Printing of coils on circuit boards
27 June 2016
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Construction of an all solid-state intense laser source at 671nm
19 April 2016
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Construction of a scalar network analyser
5 April 2016
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
Construction of a 2W TA module at 852nm
30 March 2016
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser Intensity Control with Feedback Systems
24 March 2016
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Creating arbitrary light patterns with a digital micromirror device
16 March 2016
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Hard Disk Drive Shutter System
12 Aug 2015
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Cavity setup as a close-detuned beam combiner
30 June 2015
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Production and optical transport of an ultracold gas of Rubidium atoms
8 October 2014
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
A novel transport scheme for ultracold atoms
31 May 2013
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Characterization of a Digital Mirror Device (DMD)
9 September 2014
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Creating narrow linewidth 532nm light
4 September 2014
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
MySQL database for environmental lab parameters
29 August 2014
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Single-photon nonlinearities in a Rydberg blocked BEC-cavity system
20 August 2014
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Regulation of the cooling water temperature
17 July 2014
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Generation of a single sideband by serrodyning.
12 June 2014
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Characterization of laser noise induced by an optical fiber
10 July 2013
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Towards the projection of arbitrary potentials in an ultracold Fermi gas
12 April 2013
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Engineering artificial gauge fields in time-modulated optical lattices
20 February 2013
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Characterization of a DFB laser diode
22 December 2012
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Stability Measurements of a Tapered Amplifier
22 October 2012
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Shaping optical lattice potentials with an electro-optical modulator
27 Septemeber 2012
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Assembly of DDS RF Synthesisers and Design of Firmware
1 August 2012
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Envico - Control and logging of environmental parameters via ethernet
9 July 2012
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Control Device for a tunable lens
17 June 2012
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Development of a Beam Profiler and Design of Optocouplers
1 February 2012
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Characterization of a motorized iris
11 July 2011
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Characterization of a digital PID controller
23 May 2011
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Isotope shift and hyperfine splitting of the 4s - 5p transition in potassium
15 April 2011
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity
10 April 2011
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam
23 September 2010
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Developing a mechanical shutter for optical experiments
01 August 2010
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Magneto-Optical Traps for a Second Generation Optical Lattice Experiment
Thomas Gersdorf, 07 June 2010
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.
Analytical and Numerical Semester Project
Join us for an exciting project to simulate and theoretically model a Bose-Einstein Condensate (BEC) coupled to a cavity. This system exhibits fascinating phenomena such as self-organization phase transitions, topological pumping, dark states, and exceptional points.
Together with the IMPACT team, you will develop and refine their Python-based numerical framework, which calculates the Bloch wave functions of atomes in various potentials occuring in our experminet. This enables us to employ a simple mean-field model to gain deep insights into the physics of the system. You will also contribute to further develop this underlying theoretical model.
We are seeking a highly motivated student with solid Python programming skills and a keen interest in the theory of (open) quantum systems.<\h3>
During his semester project in the Lithium team Benjamin van Ommen constructed and characterized a high transmission optical cleaning cavity for 671nm light and tested serrodyne modulation of light via a fiber phase modulator. The cavity has a free spectral range of 25.7(0.6)GHz, a FWHM linewidth of 27.6(0.3)MHz and a transmission of 76%. A stable lock with a lock bandwidth of more than 14.5kHz was achieved by acoustic insulation, thermal stabilization and compensation of mechanical resonances of the system. Using the serrodyne modulation he was able to achieve more than 33% modulation efficiency over a range of 650MHz outperforming the sinusoidal modulation.
Zhenning joined the Lithium team for his semester project to design a printed circuit board (PCB) that converts digital signals from an Ethernet cable interface into analog voltage signals using a 20-bit high-precision digital-to-analog converter (DAC), suitable for driving high-impedance loads like PID controller. Highly precise and low-noise power supply and voltage reference circuits are designed including isolation between grounds to avoid ground loops and interference between analog and digital signal lines to improve the stability and precision of analog outputs that will be used by quantum gas experiment instruments. He also developed a component managment system for Altium based on a Python webserver, an SVN repository and a MySQL database which allows sharing of component libraries among groups within the Quantum Engineering Center.
For his Master thesis Manish joined the Lattice team and worked for the first half on a theoretical project before switching to experimental work. In the theoretical part he was investigating the role of interactions in a two-frequency driving protocol for ultracold atoms in a lattice. In particular, he found conditions under which coupling processes to higher bands can be suppressed in a two-site, two-band Fermi Hubbard model. During his experimental work Manish built a test setup for investigating the possibility of optical levitation of a cloud of 40K atoms using 532 nm light. This included the setup and testing of a high power frequency doubling crystal as a light source. In addition, he characterized the beam waists and powers needed to achieve enough force to hold the atoms against gravity.
Franco joined the lithium team during his semester project to build a new laser source at 671 nm, that will be used for the Zeeman slower and in the magneto-optical trap. This new source is built by doubling the frequency of a commercial laser using two 5% MgO doped periodically poled lithium niobate crystals (MgO:PPLN) in a cascaded single pass configuration. After doing a theoretical model of the second harmonic generation he built an experimental setup. His setup achieved a doubling efficiency of approximately 40%, providing 3.1 W of light at 671 nm for an input power of 8 W at 1342 nm. It represents an improvement of more than a factor 4 compared to the previous laser source of the lithium experiment, a commercial diode laser that provided only 0.700 W of power.
Philip joined the IMPACT Team for his Semester project on implementing a fast digital notch filter on a microcontroller-based feedback device ‚LockStar’ for improved frequency stabilization in optical cavities. With this filter algorithm the device is able to cancel or modulate multiple resonant frequencies at once and deliver real-time feedback to the system. Due to the customizable initialization parameters the algorithm can be easily applied to various different situations without any additional development while reaching suppressions up to -60 dB with a sampling rate of up to 100 kHz.
Alex joined the lattice group for his Semester project to perform a theoretical study of the Floquet bandstructures arising in a 2D hexagonal shaken lattice. The focus of the project was the topology of these systems, which can no longer be characterised by the usual static invariants. In order to compute the bandstructures, a numerical script was implemented and tested on previously known results for an amplitude modulated system. Regarding the shaking scheme, the script revealed a very rich phase landscape and opened the possibility towards further work in order to obtain a phase diagram for the shaken hexagonal lattice.
In his semester thesis, Manish simulated the dynamics of localized quantum particles in a one-dimensional lattice potential. In particular, the tunneling dynamics and inter-band excitations for fast ramps of the lattice depth are studied at various timescales. This information is used to determine the time resolution of measurements done on ultracold atoms in optical lattices. Furthermore, Manish implemented the calculations of Wannier states in two-dimensional honeycomb lattices as an initial step to expand the studies of dynamics onto higher dimensions.
Mr. Patrick Helbingk joined our team to be introduced into the intricacies of electronics.
Actually he stayed longer. Much longer. He even did his final work (IPA) in our group, which
is the nifty tool to be seen on the picture : A portable Gain / Phase Analyser, aka "Gainboy".
It consists of a DDS (AD9833), a RF/IF Gain and Phase Detector (AD8302) as well as a Teensy 3.2
Microprofessor to handle user input and control the sweeps. And yes, the housing was made with
a Prusa Printer. A nice work. Thank you !
Sandra joined the Lattice team for her Master thesis on extending the current lattice setup with a near-commensurate laser at around 1064 nm. This beam allows us to create a spatially varying site offset across the extent of the atomic cloud by detuning it by a fraction of a nm with respect to the other lattice lasers. It can be used to realize topological interfaces and their corresponding edge states in a 2D optical lattice following a proposal by N. Goldman et al [Phys. Rev. A 94, 043611, (2016)]. During her work, she has built an intensity stabilization using a Lock-in technique with a bandwidth of above 10 kHz and relative intensity noise below -60 dB/Hz. In addition, the laser was locked onto a second laser using a transfer cavity limiting the relative frequency drifts to below 45 kHz for 7 hours.
Felix worked on an automated fibre coupling setup which has been previously built by Joshua Maas in his Semester project.
The basic setup consists of two motorized mirrors which can be controlled by an Arduino microprocessor. The two mirrors guide a
laser beam to a single mode fibre, where the light is coupled into the fibre for sufficient overlap between laser mode outside
and the supported mode inside the fibre. During his thesis, Felix implemented a new control flow for the mirrors using a Raspberry
Pi. In contrast to the previously used Arduino, the Raspberry Pi can run simple Python code on its processor and can be incorporated
in any Python based automation software. Furthermore, with this setup Felix demonstrated a two coupled axis optimization below two
minutes using the Kiefer-Wolfowitz algorithm, given an initial coupling efficiency of at least 14%.
on interacting Fermi gases
For his master thesis, Jeff developed and implemented methods to improve the signal-to-noise ratio (SNR) in the Lithium Team’s
experimental data. To study transport phenomena in the trapped gas, we extract the chemical potential and temperature of the
thermodynamic reservoirs from absorption images of the cloud which currently have only a modest SNR~4. This project improved
this figure by installing a better camera — an Andor iKon — into the experiment and developing image processing software to
de-noise the image based on mathematical properties of the measured data. With the iKon, the SNR is improved by a factor of
at least 3.5 — now limited by photon shot noise — and we can now image both spin states of the cloud in a single shot using
the camera’s Fast Kinetics acquisition mode. The additional steps in image processing improve the SNR by another factor of
14 and correct for some systematic errors in the imaging protocol.
During his semester thesis, Hinrich developed hardware and software to monitor various laboratory signals; and this system is termed as Laser watchdog.
In its current version it features 16 analog channels which can be connected to any laboratory output of importance. The recorded data is displayed live and
stored for later evaluation. Moreover it allows for a comparison between the recorded data and the expected form of the signals. The data acquisition is done
using a National Instruments card. The software is designed using the Matlab programming language and provides a graphical user interface (GUI) for displaying
the data of different channels, switching on and off data acquisition and selecting between different acquisition modes.
Mirco took the chance to do his "IPA" (individual personal work) in our group. He wrote a Sketch to realise an Arduino/Genuino based Spectrum Analyser up to 2.7 GHz. Together with the
built-in Reference, a nifty measurement tool is now available in our labs.
Building on previous semester theses by Sylvain and Matthias, Jeff developed a software package in Python to compute
and produce arbitrary light fields with high fidelity and efficiency using a digital micromirror device (DMD). The library
features high level functions for interfacing with the DMD, computing holograms to program on the DMD (though the method is
flexible and can be implemented with any spatial light modulator), and accurately simulating the propagation of light fields
shaped by the DMD with paraxial and exact solutions to the Helmholtz equation.
Joshua Maas developed an automated system to couple free space laser beams to optical fibers. In our group optical fibers are heavily used in all experiments. As a downside, coupling a laser beam to a fiber yields inevitable losses which mostly depend on the alignment of the related optics. An automated system can avoid the need for manual readjustments and possibly increase the speed and efficiency of the coupling process. The developed system uses four motorized screws with submicrometer resolution controlled by an Arduino running a gradient based optimization scheme, maximizing the transmitted power through the fiber. Due to its simplicity, current optical setups can be easily automized. The system is capable of optimizing a single screw position in less than a second, starting from >14% coupling efficiency. A full alignment of all four coupled degrees of freedom can be done in less than a minute.
Lena Bartha studied the effect of light tuned close to resonance on lithium-6 atoms in a transport experiment, and consider in particular the experimental realisation of a spin-dependent dipole potential. We calculate the associated light shifts in the Paschen-Back regime: via the Wigner-Eckart theorem we obtain the dipole matrix elements and lifetimes of all transitions, and use a perturbative approach to arrive at an expression for the dipole potentials and the scattering losses experienced by the different ground states. We deduce realistic parameters for a spin valve with acceptable transport losses from these results and discuss other applications of close-to-resonance beams for spin-dependent and dissipative transport. Experimentally, a new optical layout is designed and characterised in preparation of its implementation in the actual setup.
During his master thesis, Emanuel Berger worked theoretically and experimentally on the realisation of a high resolution imaging system to be implemented in the Impact experiment. He developed a light sheet to confine the atoms within the field of view of a high resolution imaging lens (NA=0.55) and tested a deformable mirror to compensate imaging distortions due to misalignments of the object from the focus point. He also implemented a feedback algorithm on the position of our dipole trap realised by means of a focus tuneable lenses. This allowed to improve significantly the stability of the final atom number in the BEC.
Kilian Sandholzer built an innovating under vacuum transfer cavity system for the IMPACT lab. This system allows to stabilize the relative frequency of an 830nm and a 785nm laser well below 100kHz. This is an essential criteria to perform stable self-organization experiments in our lab. Standard transfer cavity systems - exposing the cavity to air - are limited in relative frequency stability by the differential change of the index of refraction upon environmental changes (pressure, humidity, temperature). Under vacuum conditions, any humidity and pressure change of the air in the lab plays no role, and also temperature induced frequency fluctuations are strongly suppressed. A compact vacuum chamber hosting the transfer cavity and also a cleaning cavity has been designed and built, evacuated continuously via an ion pump. The new transfer cavity is also used to narrow down the laser linewidth of a 785nm Toptica DLpro laser to 18kHz on a timescale of 50ms.
Felix Mayor has analysed the feasibility of fabricating coils on high power printed circuit boards (PCB) in order to replace standard wound coils in cold atom experiments. Several fabrication methods were tested: various photoresist methods, toner transfer and mechanical etching. The difficulties which were encountered in the fabrication process are also described. Furthermore different tests were performed on the PCB's to check their quality. In the end it was found that some of the PCB's are able to withstand currents of 50 A without a heat sink for several seconds without failing.
Stefan Kaiser built a new laser source for cooling and manipulating atoms in our lithium lab. The standard laser source used for the lithium transition line at 671 nm rely on laser diodes and tapered amplifiers. The new design is an all-solid-state laser in an enhancement cavity providing several Watts optical power at 1342 nm contained in a single-longitudinal Gaussian mode, which is then frequency doubled to 671 nm using a commercial waveguide based doubling module. The design is based on a prototype built in Paris, and was improved with a strong focus on mechanical and thermal stabilization. Safe lasing operation is controlled by a self-made interlock system based on a Arduino Mega microcontroller.
Joël Steinemann took the chance to do his "IPA" (individual personal work) in our group. He designed an Arduino/Genuino shield which can be attached to a "Due". It upgrades it to a fully scalar network analyser, spanning the range from 25 MHz to 3 GHz. A python script does the graphical and administrational job. Dynamic range is up to 120 dB.
High power sources at suitable wavelengths are required for cold atoms experiments. For this work Benedikt Kratochwil built a laser amplifier module based on a high power chip to be employed in the cavity lab. Development on the electronic control system was performed in collaboration with Alex Frank. As a result, an interlock circuit was developed and tested. At the wavelength used in the experiment, the maximum power output obtained was 2W with a 30mW seed.
Laser intensity control is important for high precision experiments in Quantum Optics. Therefore, stable and fast feedback controllers are a key ingredient for successful experiments. There exists a wide range of controllers on the market but they are not only expensive but also often built to fullfill many different tasks lacking optimal performance for one special task. An own design of a PID controller can provide possibilities for individual special features of the controller and increase the performance. In this work a PID controller designed by Alexander Frank was tested by Kilian Sandholzer in an optical test setup and compared to a NewFocus PI controller. The PID controller was optimized for the task of laser intensity control. Measurements showed that the homebuilt PID controller can compete with the NewFocus PI controller to a certain extent.
Matthias Müller-Schrader interfaced a digital micromirror device with python to create arbitrary and dynamic light patterns. The light interacts with the atoms and creates potentials proportional to its intensity. To avoid the definition of dynamic potentials at the level of individual images he developed a python framework based on parametrised affine transformations acting on geometrical objects.
Laser shutters are often either unreliable or very expensive. Leonard Krüger developed a shutter based on the mechanics of a hard disk drive (HDD). The goal was to have an affordable solution with a fast and reproducible switching behavior. The idea is to use this pre-existing mechanical design that is perfected for long-term operation and turn it into a shutter by attaching an opaque flag to the actuator arm and drill a hole for the laser beam. The project included the mechanical design of the shutter and the development of control electronics. One special feature is that the voice coil current driving the arm is reversed half-way to minimize the impact velocity at the end stop and thus reduce vibrations and noise.
Lena Bartha finished her Bachelor thesis, during which she investigated the possibility to use an optical cavity to combine two laser beams that are detuned by only 400 MHz. With this detuning commercial optics to combine the two beams with the same polarization is not possible without large losses. In her project Lena designed two cavities with suitable characteristics and built an optical setup to test the optical cavity. Therefore a Pound-Drever-Hall technique was used for locking the cavity to the 1064nm laser. Lena showed that the two laser beams can be successfully combined and measured the stability of the system.
Thomas Karg finished his Master thesis, which he conducted on the impact experiment. He worked on the optimization of the experimental cycle, starting with a three-dimensional magneto-optical trap (3DMOT) of Rb-87, which is loaded from a 2DMOT. After sub-Doppler cooling in an optical molasses and radio-frequency evaporation in a magnetic quadrupole trap, the atoms are transferred in a hybrid trap, where Bose-Einstein condensates of 500 000 atoms are produced. The atoms could be transported by means of a novel technique based on focus-tunable lenses. Measurements of non-adiabatic transport over a distance of 20 cm have shown efficiencies up to unity along with negligible heating.
Christian Zosel developped and built a setup for the transport of an ultracold Rb cloud using tunable lenses. The transport is realized with a high power red-detuned laser system that includes intensity stabilization and utilizes a photonic crystal fiber to obtain a TEM00 Gaussian mode. Characterization of the tunable lenses showed a sufficient performance in stability, optical quality and temperature dependence. A transport procedure allowing the independent tuning of both focus position and beam waist was designed with the help of a Gaussian beam simulation software. Finally, this scheme was implemented and integrated into the impact experiment.
Sylvain de Léséleuc worked on the integration of a Digital Mirror Device (DMD) into an ultracold atoms experiment with the goal to project arbitrary and dynamic light patterns onto a two-dimensional sheet of atoms. Due to the AC Stark shift the projected laser light creates a potential for the atoms, which is proportional to its intensity. Hence, a large variety of potentials, ranging form one-dimensional channels of different length and quantum point contacts (QOC) to various types of lattices are possible if the optical projection system operates close to the diffraction limit. Sylvain showed that for the projection of extended patterns, placing the DMD in an imaging configuration is suitable. However, for tiny patterns, it is favorable to place the DMD in a Fourier plane, allowing for the correction of optical aberrations by displaying appropriate holograms on the DMD.
Raphael Bouganne finished his semester thesis, during which he built a stable narrow linewidth highpower 532nm laser. Optical lattices require stringent optical properties, mainly phase stability of the laser light. Commercial high power lasers at a wavelength of 532nm have a linewidth which is to high to be useful for an optical lattice setup. Therefore a frequency doubling setup for a narrow line 1064nm laser was built in this project. The generated second harmonic light is then used as a reference to frequency lock the existing high power 532nm laser. Raphael showed that the linewidth of the original laser was reliably reduced by a factor of 50 with this scheme.
hi Zhang finished his semester thesis, during which he built a MySQL database to store laboratory environmental parameters. Knowing the environmental parameters well is important for highly sensitive experiments. The Envico framework provides a flexible way to have the environmental parameters measured. However, for long-term trend analysis of those parameters, it is also important and useful having the measured data well organized and making a user friendly interface to ease the reading and plotting of data. In this project a database based on MySQL is set up to store the measured data as well as auxiliary informations in an efficient manner, and a graphic user interface is built to make plotting the data of any desired sensor easier. Moreover, basic data analysis functions like calculating correlations and low-pass filtering of data are also included.
Nishant Dogra worked both theoreticall and experimentally towards the creation of single-photon nonlinearities in a Bose-Einstein condensate coupled to a high-finesse optical cavity. This system exploits the large cooperative coupling of many atoms coupled to a cavity mode. The non-linearity is then introduced via single Rydberg excitations which block any further excitation within a certain blockade radius. Nishant was theoretically exploring this syste and set up the coupling laser at 480nm.
Stefan Kaiser finished his semster thesis in which he built a cooling watr temperature stabilization. At our lithium experiment, the variation in temperature of cooling water causes an additional error source requiring a cooling water control system. The cooling water is heated up by using a heat pipe and is regulated at a specific target temperature by performing a Proportional-Integral-controller. Thus the standard deviation of the mean temperature is measured to be approx. 0.020 °C. Without any regulation the standard deviation equals about 0.060 °C. The performed PI-controller is close to the best possible solution, since the sensor has a quantization error of 0.018 °C.
Manuel Chinotti tested an electric sawtooth generator that was developed in our group. It is used for single laser sideband generation by frequency modulation of an Electro-Optical modulator. This technique is called Serrodyning. It was possible to generate a single sideband with a high efficiency comparable to previously reported results which used non-linear transmission lines for the sawtooth generation, which are not commercially available no more.
Frederik Lohof investigated the polarization distortion and the frequency noise of a laser induced by optical fibers. The effects have been known to be sensitive to the laboratory environment and thus it has been necessary for us to quantify them. The polarization distortion was examined by making use of various polarization optics. A high-resolution heterodyne spectroscopy was performed to resolve the phase noise of the laser behind the fiber and he successfully resolved the frequency broadening of several Hz. He also carried out the examination on a couple of fibers to characterize each of them.
Dominik Husmann tested the imaging quality of several light sources of differing coherence categories in a diffraction limited system. By illuminating a binary transmissive mask, structures on the scale of the diffraction limit were projected and imaged in a test setup simulating the microscope system in the Lithium experiment. The quality of the structures showed strong dependences on spatial and temporal coherence properties of the illuminating light, especially in terms of the sensibility to defects in the optical path. Such a projective setup can be used to create arbitrary potentials in the channel recently realized in the Lithium transport experiment. The results classify the different light sources in terms of their suitability for the implementation in the Lithium experiment. Additionally the transport properties through several channel potentials were simulated numerically. The results are a step forward to probing mesoscopic transport phenomena in cold atoms systems in order to simulate analogous transport phenomena of electrons in solids.
Martin Lebrat looked at practical ways to generate articial gauge fields in an optical lattice by modulating its potential or subjecting it to a homogeneous force in a time-periodic manner. Numerical simulations confirm that modulations that break time-reversal symmetry may renormalize tunnel couplings which can take on complex values; in turn, their phase can be understood as the gain of an Aharonov-Bohm phase under a fictitious magnetic field while hopping between lattice sites. On the experimental side, such modulations could be produced using electro-optic modulators or piezo-electric plates, whose dynamical behavior was also characterised. In the 2D honeycomb lattice similar to graphene) which we can simulate here in the Quantum Optics group, this will facilitate the implementation of the celebrated Haldane model exhibiting a topological transition between different quantum Hall phases under a staggered magnetic field. The observation of such phases would be a great step towards the simulation of topological insulators with cold atoms.
Christian Zosel characterized a DFB laser diode with respect to its applicability in quantum optics experiments. In distributed feedback (DFB) laser diodes, the frequency selection is realized with a Bragg grating inside the active layer of the diode. This design is very robust and offers good mechanical stability, since there is no external element. DFB diodes are tunable via laser current and temperature and have a typical linewidth of 1-4 MHz. In addition, they are cheaper than extended cavity diode lasers. The characterization included stabilizing the laser frequency to an atomic transition (spectroscopy lock) and to an external reference signal (offset lock). Furthermore, the phase response of the entire laser system was studied to assess the possibility of setting up a phase locked loop.
Karin Fisher has investigated how fluctuations in temperature and seed power as well as mechanical deformations affect the output of a tapered amplifier. Tapered ampli?ers are an important tool in the ?eld of ultracold atoms as they enable the ampli?cation of coherent laser light to higher powers for applications such magneto-optical traps. The dependence of output power on temperature shows a reproducible threshold behaviour, which could be identified as the crucial factor currently limiting the stability of tapered amplifiers.
Martin Lebrat has finished his semester thesis!
Modulating an optical lattice periodically in time could help implement new kinds of effective Hamiltonians that are not accessible by simply tweaking the static parameters of the potential. In this semester thesis, we explore a new way to shape the potential landscape of an optical lattice by introducing an intensity mismatch between the counter-propagating beams that make it up, and study what band structures and tunnel couplings such new potentials yield. A practical solution to create the desired mismatch would be to manipulate the polarisations of the beams with electro-optic modulators; lithium niobate based modulators have been modelled and tested in a small scale setup.
Tobias Kittelmann took the chance to do his IPA / LAP in our group. The project consists of a modular DDS Synthesiser. Using modern layout tools, a printed circuit board had to be designed. Assembly as well as debugging the board led to the design of the firmware. Some sophisticated subroutines even allow the self calibration of the device. Ethernet capability as well as lock on external 10 MHz make this a handy and useful device.
Florian Vogelbacher designed and implemented a complete hard- and software framework to measure in a flexible way environmental parameters like temperature, humidity or water flow in our laboratories. The acquired data is stored via ethernet on a Xymon/hobbit monitoring and database system, able to send out alarm messages via sms and email if parameters are out of a specified range.
Samuel Häusler developed a control device to steer a tunable optical lens with which we want to manipulate ultracold atoms. His design is based on a mbed microcontroller which stores the calibration curves of the lenses and implements a PID-feedback loop regulating the current fed to the lens.
Matthias Bucher developed a C++ software to perform live characterizations of laser beams using inexpensive and small CCD cameras from PointGrey. The software allows for fitting the laser beam intensity profile and tracking of the beam position.
Additionally, new digital and analog optocouplers have been constructed and characterized during the course of the thesis.
Arne Hansen finished his Semester thesis!
We explored a possibility to continuously change the trap frequencies of an optical tweezer in order to control the Fermi energy of trapped Lithium atoms. To this end, a motorized iris was characterized with respect to intensity noise and changes in shape of the propagating beam. The measurements show no severe disturbance of the optical tweezer.
Pirmin Weigele finished his Semester thesis!
A digital PID controller was characterized and compared to an analog PID controller. To this end a diode laser was stabilized to an atomic transition using a frequency modulation spectroscopy and one of the PID controllers. Several settings of the PID controllers were tested and the frequency fluctuations of the laser were recorded with the according locks.
Alexandra Behrle finished her Semester thesis in the group of Dr. Michael Koehl at University of Cambridge, UK!
The dependence of optical transition frequencies between electronic states in atoms on the properties of the nucleus is among the most frequently investigated questions in laser spectroscopy. We have measured the hyperfine splitting of the 5P1/2 state of 40K and determined the isotope shift of the 4S1/2 -> 5P1/2 transition, exceeding the previously achieved accuracy for the low-abundance isotope 40K by one order of magnitude. Our results contribute to determining the atomic structure of potassium more accurately.
Laura Corman finished her Semester thesis!
In this semester project, the possibility to create Schrödinger cats (or macroscopic superposition of states) in an experimental setup consisting in a Bose-Einstein condensate pumped with a side laser and put in a cavity is investigated. As this system has been proven to realize the Dicke Hamiltonian, this Hamiltonian is studied in particular, but only on timescales on which dissipation - mostly induced by the cavity - is negligible. In addition, the various orders of magnitude of the experimental parameters allows for simplifications that lead to precise conditions to create Schrödinger cats.
Matthias Bucher finished his Semester thesis!
We have set up a PID control for spatially stabilizing a laser beam using a field programmable gate array (FPGA) by National Instruments. The programming language used was LabVIEW9 SP1. Jitter and drifts of the laser beam were effectively reduced by a factor of about 10, confining the remaining oscillations to an interval of roughly 2 μm around the intended center.
Frieder Lindenfelser finished his Semester thesis!
To reach ultra low temperatures atoms can be cooled using laser-light. Usually this cooling happens in two stages: The atoms are slowed down by the optical Doppler effect, and then evaporatively cooled in a dipole trap. Switching between these two stages means blocking one set of laser-beams, and letting pass another within some microseconds, so the atoms will not get lost. This is one possible application among many, for which a mechanical shutter was developed.
Thomas Gersdorf finished his Bachelor thesis!
This work focuses on the implementation and the testing of a laser setup for magneto - optical traps (MOTs) for potassium atoms. Two different types of MOTs, namely a 2D and a 3D MOT, will be used for the initial trapping and cooling of 40K and 39K atoms in a second generation optical lattice experiment which is currently being set-up in the Quantum Optics group at ETH Zurich.
Using components developed and pre-aligned in previous work, the laser set-up has been completed and optimized for stable and continuous operation. A new design for eletro-optic modulators (EOMs) has been developed as part of this procedure. This new modulator design works with high efficiency even at modulation frequencies above 1 GHz and may be used in future experiments requiring EOMs with these high modulation frequencies.
The laser setup is now ready to be used in the new experiment for MOTs with 39K and 40K. Its proper operation has been demonstrated in this work by loading 39K from a cold atomic beam generated in the 2D MOT into the 3D MOT. Furthermore, the system was optimized such that a successful MOT operation can be achieved within less than half an hour after switching on the system without any additional tweaking.