Wir bieten regelmässig Master und Bachelorarbeiten in unserer Gruppe an. Wenn du in die Gebiete Quantenoptik und ultrakalte Quantengase einsteigen und diese spannenden Forschungsfelder kennenlernen möchtest, dann ist das eine ideale Möglichkeit. Im Rahmen einer Semesterarbeit kannst du erste Erfahrungen im Forschungsalltag unserer Gruppe sammeln und dabei selbständig über einen Zeitraum von ca. 6 Wochen an einem Projekt arbeiten. Die Semesterarbeit wird am Ende mit einem schriftlichen Bericht abgeschlossen. Themen für mögliche Projekte umfassen Elektronikentwicklungen, optische Aufbauten, Softwareprogrammierung, Vakuumtechnologie und vieles mehr. Experimentelle Grundkenntnisse sind dabei sehr hilfreich, und lassen sich zum Beispiel im Rahmen des Vorgerückten-Praktikums und insbesondere der Advanced Students Labs gewinnen. 

Melde dich und lerne unsere Gruppe kennen, wir freuen uns von dir zu hören!
Kontakt: Tilman Esslinger und Tobias Donner

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

Do not hesitate to contact us and meet our group, we are looking forward to hearing from you!
Contact: Tilman Esslinger and Tobias Donner

13. Sep 2017

Automated fiber coupling

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.

12. Apr 2017

Towards spin-dependent optical potentials

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.

29. Mar 2017

Towards a high resolution imaging system for ultra cold atoms in two crossed cavities

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.

30. Jun 2016

Construction of a transfer cavity

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.

27. Jun 2016

Printing of coils on circuit boards

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.

19. Apr 2016

Construction of an all solid-state intense laser source at 671nm

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.

5. Apr 2016

Individual personal work: construction of a scalar network analyser

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.

30. Mar 2016

Semester thesis: construction of a 2W TA module at 852nm

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.

24. Mar 2016

Semester thesis: Laser Intensity Control with Feedback Systems

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.

16. Mar 2016

Creating arbitrary light patterns with a digital micromirror device

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.

12. Aug 2015

Semester thesis: Hard Disk Drive Shutter System

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.

30. Jun 2015

Bachelor thesis: Cavity setup as a close-detuned beam combiner

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.

8. Oct 2014

Master Thesis: Production and optical transport of an ultracold gas of Rubidium atoms

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.

31. May 2013

Master Thesis: A novel transport scheme for ultracold atoms

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.

9. Sep 2014

Semester Thesis: characterization of a Digital Mirror Device (DMD)

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.

4. Sep 2014

Semester Thesis: Creating narrow linewidth 532nm light

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.

29. Aug 2014

Semester thesis: MySQL database for environmental lab parameters

Chi 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.

20. Aug 2014

Master thesis: Single-photon nonlinearities in a Rydberg blocked BEC-cavity system

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.

17. Jul 2014

Semester thesis: regulation of the cooling water temperature

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.

12. Jun 2014

Semester thesis: generation of a single sideband by serrodyning.

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.

10. Jul 2013

Semester thesis: Characterization of laser noise induced by an optical fiber

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.

12. Apr 2013

Master thesis: Towards the projection of arbitrary potentials in an ultracold Fermi gas

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.

20. Feb 2013

Master thesis: Engineering artificial gauge fields in time-modulated optical lattices

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.

22. Dec 2012

Semester Thesis: Characterization of a DFB laser diode

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.

22. Oct 2012

Semester Thesis: Stability Measurements of a Tapered Ampli?er

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. 

27. Sep 2012

Semester Thesis: Shaping optical lattice potentials with an electro-optical modulator

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.

1. Aug 2012

IPA / LAP: Assembly of DDS RF Synthesisers and Design of Firmware

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.

9. Jul 2012

Semester Thesis: Envico - Control and logging of environmental parameters via ethernet

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.

17. Jun 2012

Semester Thesis: Control Device for a tunable lens

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.

1. Feb 2012

Master Thesis: Development of a Beam Profiler and Design of Optocouplers

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.

11. Jul 2011

Semester Thesis: Characterization of a motorized iris

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.

23. May 2011

Semester Thesis: Characterization of a digital PID controller

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.

15. Apr 2011

Semester Thesis: Isotope shift and hyper fine splitting of the 4s - 5p transition in potassium

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 hyperfi ne 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.

10. Apr 2011

Semester Thesis: Deterministic generation of Schrodinger cats in a Bose-Einstein condensate placed in a cavity

Generation of atom-light entanglement

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.

23. Sep 2010

Semester Thesis: Implemention of a PID Control on an FPGA to Spatially Stabilize a Laser Beam

Casing with hardware inside

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.

1. Aug 2010

Semester Thesis: Developing a mechanical shutter for optical experiments

The final shutter design

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.

17. Jun 2010

Bachelor Thesis: Magneto-Optical Traps for a Second Generation Optical Lattice Experiment

Potassium atoms in the MOT

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.