Finished projects

Here you find a small collection of previous student projects. We hope you get inspired! If you are looking for a project, check out our project page.

Experiment control for new experiment

Tore Homeyer, bachelor project 2022

The aim of my bachelor’s thesis was to set up the experiment control system for the Hybrid Quantum Optics (HQO) experiment. I worked in the hybrid quantum optics team together with Hannes Busche, Cedric Wind, Julia Gamper, and Florian Pausewang.

During my project I adapted the existing systems from other experiments in the group to the new HQO infrastructure. This included a good amount of Python programming for communication with various devices like pulse generators or function generators used to run the experiment once it is built, as well as some electronics work.

I learned a lot about the thoughts that go into designing and building a new experiment and the requirements of the supporting systems. Additionally, I gained insights into how to „talk“ to various instruments using Python scripts, which is of course very useful for any future labwork.

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Tore did his project on the experiment control system for the Hybrid Quantum Optics project

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The experiment control system involves communication between many different devices

Measurement of dye concentrations in liquids using FFPCs

Jasper Schwering, bachelor project 2022

During my Bachlor project I worked in the Fiber Cavity Optomechanics group together with Lukas Tenbrake, Hannes Pfeifer and Florian Giefer.

In our team we work with so called „Fiber Fabry-Perot Cavities“ (FFPC). These FFPCs consist of two fiber mirrors opposing each other inside a glass ferrule as you can see in the picture on the right. The fiber mirrors are fabricated from bare glass fiber, where a high reflective coating is placed onto the fiber ends. The cavity length of the FFPCs can be controlled via the piezoelectric element, which is glued to the glass ferrule. This way the finesse of the cavity can be measured by scanning over the cavity length.

FFPCs have a broad area of aplications. One of them is the research on optomechanics, which is the main topic of the FCO group. Another one is using the FFPC as a spectrometer, as it was previously performed in our group for oxygen spectroscopy.

The aim of my project was to transfer the spectroscopy application to liquids, starting with the invastigation of the finesse change inside of different dye concentrations. The used solutions were made form a near-infrared dye mixed with destilled water. An FFPC was placed inside of such solutions and the finesse change due to the additional absorption losses was analyzed (compare the picture on the right).

During my research I had to do a lot of practical work, such as building several FFPCs, arranging optical setups or preparing the dye concentrations, but also finding solutions for various problems arising in the process of my project. Also some coding was done for results analyzation. Overall I made the first steps towards realizing this specific FFPC application, and I charaterized the main problems of measuring liquid concentration.

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Jasper did his project in Fiber Cavity Optmechanics team.

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A FFPC with its glass ferrule on the bottom containing the two opposing fiber mirrors, above the piezoelectric element.

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Petri dish with dye solution inside, containing the FFPC in the middle.

Laser frequency stabilization for Rydberg excitation

Florian Pausewang, bachelor project 2022

During my Bachelor project I joined the hybrid quantum optics team and worked with Hannes Busche, Cedric Wind, Tore Homeyer, and Julia Gamper.

I continued the work on the laser system of the hybrid quantum optics project, following in the footsteps of Julia. One of the steps of this HQO experiment is the excitation of rubidium atoms to Rydberg states (states with a high principal quantum number), which have a long lifetime and therefore a narrow linewidth. The prerequisite for a long coherence time of the cooled and excited atoms is that the lasers used in the process have a linewidth comparable to or smaller than the linewidth of the transition.

Two lasers at 780 nm and at 960 nm are used for the Rydberg excitation. My task was to narrow the linewidth of the 960 nm laser by locking it to a high finesse cavity. The ultra low expansion cavity which we use provides a very narrow and stable reference frequency. I performed many optimization-iterations of the feedback-loop that corrects the laser freqency to achieve a small linewidth.

By using a beatnote between two independent lasers, locked at the same frequency to different cavities, the linewidth of the locked locked lasers could be quantified below 1 kHz and a longtermdrift under 5 kHz in 12 hours.

These stabilized lasers can be used to perform the next steps towards producing Rydberg atoms.

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Florian did his project on the laser system for the Hybrid Quantum Optics project

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The beatnote signal between two lasers show how the lock optimized by Florian narrows the linewidth.

Tailored light potentials with a SLM

Jan de Haan, bachelor project 2022

My bachelor thesis was about setting up a liquid crystal on silicon spatial light modulator (SLM). This device can imprint a freely choosable spatially varying phase shift onto light. The goal was to use it to create arbitrary intensity patterns and to characterize the results. In the future, the intensity patterns created with the SLM will be used for optical dipole trapping of atoms in the Rubidium Quantum Optics (RQO) experiment.

I really enjoyed working with Nina Stiesdal, Lukas Ahlheit and Simon Schroers in the RQO-lab, and got to learn a lot about the RQO experiment.

Over the course of my thesis, I built an optical setup for testing the SLM, including setting up the laser that will provide the light for the dipole traps that will be made with the SLM in the future, wrote various pieces of software to display phase patterns on the SLM, compute those phase patterns in the first place, and optimize the results iteratively.

The project was a nice mix of learning about how to build optical setups, applying Fourier optics and understanding and implementing algorithms and methods for finding and improving phase patterns to display on the SLM.
The results are both the tangible spot intensity patterns of high quality that can be made with the SLM, as well as knowledge of what factors of an optical setup including an SLM influence the image quality.


Jan did his bachelor project in the rubidium quantum optics team, and worked on tailoring light potentials with a SLM.

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The device itself: The liquid crystal on silicon spatial light modulator.

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An example of a simple spot array that could be used for trapping atoms.

A Vacuum Fiber Microscope

Florian Giefer, bachelor project 2022

I did my bachelor thesis in the “Fiber Cavity Optomechanics” project. In the FCO group, we are examining the behavior of mechanical oscillators, placed inside fiber Fabry-Perot cavities. These fiber Fabry-Perot cavities consist of a fiber mirror (optical glass fiber, coated with a Bragg reflector) and a mirror substrate.
It is advantageous to observe these oscillators in vacuum, as the absence of air dampening improves their mechanical quality.

Additionally, we are interested in the behavior of interconnected resonator assemblies, as this could enable advances in optomechanical circuits and quantum computing. This led to the idea of my project, the “Double Tip Vacuum Fiber Microscope”, an apparatus capable of precisely placing two fiber mirrors on
top of a mirror substrate to form fiber Fabry-Perot cavities in vacuum. You can see what this setup looked like in the image on the right. Central components are the five electrically controlled translation stages (seen in black), as well as the fiber holders (aluminum block on the leftmost stage). The Fiber holders allow for a scan of the cavity length via an integrated piezo element.

I was very thankful for the possibility to work on such an interesting experiment together with Lukas Tenbrake and Hannes Pfeifer, who both are great teachers and advisors. My project involved lots of practical skills for assembling the experiment and vacuum setup, like screwing and gluing components together, planning the workflow, prototyping experiment parts, and testing the setup, as well as some
coding for a control software of the experiment.

This picture shows a fiber mirror over an array of polymer resonators in the fiber microscope.

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Florian built a vacuum fiber microscope during his bachelor project.

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The experimental setup, consisting of five translation stages (black), carrying a fiber mirror in a fiber holder (left) over a mirror substrate.

Raman Sideband Cooling of Rubidium

Simon Schroers, bachelor project 2022

During my bachelor thesis I was working on the Rubidium Quantum Optics project together with Lukas Ahlheit, Nina Stiesdal, and Jan de Haan.

Even though the main topic of my thesis was Raman sideband cooling, we worked together on all the different parts of the experiment. This means we had to tackle various problems arising during the build-up and improvement on different parts of the setup.

This way I got an insight into all the different parts of experiment and an understanding of modern atomic physics reasearch. This is not just measurements and working at a computer, but also building optical setups using a screwdriver and fine alignment of the optics. Therefore, there was a broad range of tasks that needed to be done, and I never got bored.

For the Raman sideband cooling, which in the end was the main part of my project, I had to set up optics in order to create an optical lattice and prepare different laser beams in order to be used on our atomic cloud of rubidium atoms. To implement the cooling I had to do several adjustments  e.g. a power stabilization for the optical lattice and compensation magnetic stray fields using microwaves.

In the very end of my project, I was able to implement and optimize the Raman sideband cooling of Rubidium atoms. With the cooling scheme we can lower the temparture by a factor of 16. Using the cooled atoms it will be possible to do experiments using Rydberg excitation and a lot of cool nonlinear optics-experiments.

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Simon did his project on among other things Raman sideband cooling of Rubidium.

A series of absorption images of rubidium atoms after releasing them from the optical dipole trap. The atomic cloud expands after being released, and depending on how fast the cloud expand, we can extract the temperature of the atoms.

The two different animations are for different temperatures.

Laser frequency stabilization for laser cooling of Rb atoms

Julia Gamper, bachelor project 2022

For my Bachelor thesis I was able to work as a part of the Hybrid Quantum Optics project together with Hannes Busche and Cedric Wind.

The aim of my project was to build the laser locking setup for the lasers at 780nm which includes a reference laser and two lasers which are going to be used in a magneto optical trap (MOT). Therefore I built the needed optics and electronics to make this possible.

First of all, one of the three lasers has been frequency stabilized onto an ultra-stable external reference cavity. This stabilized laser can then be used as reference for additional lasers at 780nm e.g. for the two lasers which are going to be used in the MOT.

These two lasers need to be stabilized with a certain frequency offset to make sure they are at the transition needed, one for exciting the Rubidium atoms and the other one is going to be used as a repumper. This is why the lasers are phase-locked relative to the reference laser.
It is now possible to use the lasers in the MOT as soon as it is built and the reference laser can also be used as a reference for additional lasers at 780nm e.g for the first step in Rydberg excitation.

Julia Gamper
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Julia did her project on the laser system for the Hybrid Quantum Optics project

Hybrid Quantum Optics laser system

A close look at the Hybrid Quantum Optics laser system.

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