Bachelor- and Master-projects

In our YQO experiment, lasers with different wavelengths are locked to an ultralow expansion reference cavity. Other lasers are frequency stabilized by so-called offset locks relative to the cavity-stabilized master laser. The laser to be locked interferes with the master laser and the generated beatnote at hundreds of MHz is compared to a reference signal. An error signal is generated by a digital phase lock box, then sent into a PID controller that gives a feedback signal to the laser to correct any frequency drift.

In this project, you will implement an upgraded a beatnote lock system extending the achievable frequency range of our blue lasers. For that, new ideas in the RF electronics will be tested. For feedback loop optimization, you will use advanced interferometry to measure frequency noise.

The goal of this project is to design, build, and integrate an absorption imaging system capable of detecting Rydberg atoms in close proximity to the surface of an atom chip. Rydberg atoms are extremely sensitive quantum systems, and operating them near a surface presents unique challenges for both optical access and imaging fidelity. To overcome these challenges, we aim to develop a tailor-made imaging setup that provides the required spatial resolution, stability, and control while remaining fully compatible with the constraints of our current experimental apparatus.

Your work will involve the implementation of the imaging system: from the conceptual and optical design, through building and aligning the setup, to characterizing its performance under realistic laboratory conditions. This includes evaluating optical aberrations, optimizing detection efficiency, and ensuring that stray fields or surface effects do not compromise the measurement of Rydberg-state populations.

The field of Rydberg quantum optics explores how a few-photon probe field can be manipulated using the strong interaction between ultracold atoms in Rydberg states, which are mapped onto photons and give rise to photon-photon interactions.  Until now, the Rubidium team has explored a one-dimensional regime of photon-photon interaction, but recently, we have implemented a single-photon sensitive camera to detect transverse interactions.

To detect transverse interactions between probe photons, it is crucial that the probe beam is a near-perfect Gaussian, but since the beam is focused to less than 10 µm, the beam characterization is non-trivial.

In this project, your task will be to once and for all build a portable beam profiler which will allow beam characterization with high precision. The beam profiler will be based on a microscopic pinhole on a motorized precision stage, and you will use your new device to test lenses for the next generation Rubidium quantum optics experiment.

The Bonn Fiber Lab develops fiber-based microcavities using laser ablation, with applications for example in coupling to cold atoms, semiconductors, micromembranes, and gases.

One of our current goals is to better understand the performance of our fabrication setup and the ablation process to further improve the quality and reproducibility of our structures.

Student projects could involve a detailed characterization of the setup’s accuracy and stability, or the implementation and testing of a method to reduce debris formation during ablation, which remains a key factor limiting the attainable finesse of fiber cavities.

(Top) Fabrication steps: A fiber is cleaved, shaped with CO₂-laser pulses, inspected by interferometry, and finally coated to form a curved mirror.

(Bottom) Setup: CO₂-laser machining setup with integrated interferometer for fabricating and characterizing curved fiber surfaces.

The goal of the hybrid quantum optics project is to realize hybrid quantum systems of ultracold Rydberg atoms and superconducting quantum circuits operating in the microwave regime. In particular, we want to study the coupling between an electromechanical oscillator near its quantum ground state. This requires cooling macroscopic objects to just a few K using liquid He cryostats. However, closed-cycle cryostats typically suffer from vibrations in the µm range that are induced during He compression, and they offer limited optical access due to the radiation shields that protect samples from the thermal blackbody environment. Both of these are typically incompatible with ultracold atom experiments, which rely on good access to control, manipulate, and detect them.

Soon, we will receive a commercial cryostat that provides a suitable environment for both. For example, vibrations will be damped by a special vibration isolation system, and atom trapping will be achieved with magnetic rather than optical traps. In this project, you will test and characterize crucial components and properties of the system, such as vibration isolation, the electrical performance of superconducting chips, or the system’s cooling performance, and join us in producing the first ensembles of ultracold Rb atoms in a 4 K environment.

The Rubidium Rydberg Quantum Optics experiment is the oldest experiment in our research group, and it is getting a glow-up! The main focus of this experimental setup has been to use the Rydberg blockade to turn small clouds of ultra-cold rubidium atoms into effective two-level systems, so-called Rydberg superatoms that couple strongly to weak probe pulses. So far, the probe pulses were simply sent through the cold atoms and detected. However, implementing a three-mirror optical cavity around the superatom system will allow us to reach stronger light-matter interactions.

In the next iteration of the experiment, we will build the cavity, and we will also upgrade the atom preparation by constructing a 2D MOT for pre-cooling of atoms. This requires major changes of the vacuum system and new considerations for optics surrounding the chamber.

In this project, you will work with the PhD student on designing and, if time allows, building the upgraded experimental setup, focusing on the 2D MOT.

Modern experiments in quantum optics (and virtually any other area) require the automated control of many interlinked output devices as well as precisely timed data recording. This is achieved by the combination of dedicated real-time computing hardware and custom-tailored control software. Features often include automated data taking for many days and experiment parameter adaptation via feedback, maximizing the possible data acquisition rate.

In this project, you will implement new computer control software in Python building on established concepts and hardware in our labs. This will combine device control, graphical user interface and network communication to automate the running of complex quantum optics setups.