Bachelor- and Master-theses

Stable fiber Fabry-Perot cavities (FFPCs) are a versatile platform for light-matter interaction. In the Bonn Fiberlab we develop advanced FFPCs with high stability and extended functionalities for spectroscopy, sensing, as emitter interfaces and for other applications.

Projects in our lab deal with developing advanced FFPC devices, fabrication of specialized FFPCs and proof-of-principle experiments for applications of FFPCs e.g. as miniaturized spectrometers of sensors.

Cavity optomechanical experiments facilitate the interaction of light with mechanical resonators for example for force-sensing, wavelength conversion or for investigating many-body physics. In our experiments we use fiber Fabry-Perot cavities to interface polymer drum resonators fabricated via 3D direct laser writing.

Projects in our lab range from setting up vacuum integrated fiber cavity microscopes over resonator design and fabrication optimization to experiments on optomechanical multimode systems.

Rydberg atoms offer an interesting platform to realize strong optical nonlinearities due to the long-range interactions between Rydberg atoms. These interactions can make small atomic ensembles in optical traps behave collectively like single emitters - so-called Rydberg Superatoms.

Very flexible optical dipole traps can be realized with either a Spatial Light Modulator (SLM) or an acousto-optical deflector (AOD). A SLM modifies the phasefront of an incident beam, and can be used to create holographic intensity patterns and thereby shape optical potentials. An AOD on the other hand deflects a beam in one direction at an angle determined by an applied frequency. Where a SLM offers a high degree of freedom in terms of shaped potential an AOD offers speedy changes of potentials.

This project focuses on the realization of optical traps for Rydberg superatoms using a combination of a SLM and an AOM. Your task will be to design and build a testing setup to characterize the combined SLM-AOD system, and the optical traps which can be realized with it, and then to implement your setup in the existing experiment.

The long-range interaction between Rydberg atoms enables otherwise difficult manipulation of single photons as single photons can be mapped onto interacting atomic states. This has been demonstrated in many experiments using the rubidium Rydberg machine in the Nonlinear Quantum Optics group. The machine had the last update in 2015 and since then it has produced many important scientific results.

In the meantime the state of the art of ultra-high vacuum chambers has developed significantly: glass cells with long glass-to-metal transitions can be replaced by windows glued in titanium frames. In the light of this development, the NQO rubidium Rydberg setup needs an overhaul.

This project focuses on designing the next generation of rubidium Rydberg vacuum chamber to be manufactured by the in-house workshop. This involves designing and assembling a new ultra-high vacuum chamber with a titanium-framed glass cell and built in electric field control. You will of course work closely together with the PhD’s and postdocs during the design process, and you will get to work on the existing setup on the side.

Alkaline-earth type atoms with two valence electrons exhibit richer physics than traditional alkaline atoms for many ultracold applications. Yb atoms offer a broad singlet transition, (6s2)1s0 to (6s6p)1p0 with a linewidth of ~28 MHz and a narrow triplet transition (6s2)1s0 to (6s6p) with a linewidth of ~182 KHz. Utilizing these we have built  a compact two color 2D-3D MOT setup which loads a large number of atoms at sub-Doppler temperatures. With the implementation of a new cooling scheme (Sawtooth Wave Adiabatic Passage - SWAP) high phase-space densities are achieved. In the next steps, we aim to integrate the already assembled optical dipole trap and the Rydberg excitation and probe setup into the experiment to realize Rydberg EIT (Electromagnetically Induced Transparency) in Yb. Afterwards, we aim to implement an EIT based quantum memory as a first step.

Your tasks will include integrating the optical dipole trap and Rydberg excitation setup and working towards realizing the EIT in Yb.

For most practical purposes photons are interaction-less. Non-linear quantum optics opens a way to manipulate and create interactions between single photons. In our project we will be using Yb Rydberg atoms as a non-linear medium in a process called EIT. The ongoing single photons can interact and result in the exchange of the information stored among them. Usually, these interactions are observed and interpreted by counting the exiting photons and thus looking at the intensity aspects. We establish a setup for measurements of the phase shifts imprinted on the single photons.

In this project your task is to build the phase interferometer with a single photon source. You will be using various components to set up, detect and store the signals.

Cavity optomechanical experiments facilitate the interaction of light with mechanical resonators for example for force-sensing, wavelength conversion or for investigating many-body physics. In our experiments we use fiber Fabry-Perot cavities to interface polymer drum resonators fabricated via 3D direct laser writing.

Projects in our lab range from setting up vacuum integrated fiber cavity microscopes over resonator design and fabrication optimization to experiments on optomechanical multimode systems.

In the Hybrid Quantum Optics project, we are planning to interface ultracold Rydberg atoms with photonic and superconducting RF circuits, which requires experiments to take place inside a cryostat. In previous experiments, we have realized the trapping potentials for ultracold atoms using optical dipole traps created from high power laser beams. Inside a cryostat this is no longer an option: Heat shields that protect objects inside the cold region from blackbody radiation, limit the optical access and even stray reflections from the high power beams can lead to unwanted heating of both the shields and the cooled objects.

In this project, you will implement and optimize combinations of magnetic and optical traps and cooling techniques to produce samples of over 10^6 atoms at temperatures of ~ 1 µK inside a cryostat. The atoms will be prepared in a magneto-optical trap and then be transported into the cryostat using movable magnetic traps. Once inside the cryostat, we plan to trap the atoms using magnetic fields produced by a superconducting atom chip. It will be your task to design the chip and optimize the interplay of different traps and cooling techniques to produce large and cold atomic ensembles.

Experiments combining ultracold atoms and single photons to study fundamental aspects of quantum optics and to explore quantum technology applications require a large number of commercial and self-built individual devices - lasers, cameras, single-photon-detectors, optical elements, signal sources, data acquisition devices,... - to be precisely synchronized and ideally controlled through a user-friendly graphical interface (from the beach).

In the NQO group, a standardized solution used by our different labs as well as by others has been developed and maintained for years. Rapid progress in fast digital and analog control hardware now offer new opportunities that make it more sensible to develop a fully new version for the future. In particular, various open-source options now exist that can be co-developed with other research groups, but also adapted to our specific experiments.

For this project, we are looking for a programming enthusiast interested in joining such a development effort, which still is closely involved with the science and technology of a cold-atom experiment.