Bachelor- and Master-theses

We are always offering Bachelor- and Master-projects. Below you can find current project ideas.

Our work combines aspects of modern optics, ultracold atomic gases, and Rydberg physics. Working in an experimental group like ours means you will be fully integrated in one of our lab teams and your project will be closely related to on-going research. If you are interested in one of the projects you see, or you would like to hear more about other options, do not hesitate to get in touch via email. You are also very welcome to simply visit our labs.

Project ideas fall 2022

Applications of advanced fiber Fabry-Perot cavities

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.

What you will learn: Set-up of fiber-optic experiments, manufacturing of FFPCs

Little drum
© NQO

Size comparison of a monolithic FFPC device with two fiber mirrors in a glass ferrule sitting on a tuning piezo.

Fiber Fabry-Perot cavities meet 3D direct laser writing

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.

What you will learn: Set-up of fiber-optic experiments, numerical and experimental investigation of mechanical resonators, vacuum experiment techniques

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Fiber mirror approached to polymer structures on a macroscopic mirror in a single tip fiber-cavity microscope.

Shaping optical potentials for single atoms and Rydberg superatoms

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.

What you will learn: Designing and building advanced optics setups, software-hardware interfacing, cool physics, thinking in Fourier space

  • To be announced
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Fiber mirror approached to polymer structures on a macroscopic mirror in a single tip fiber-cavity microscope.

Next generation waveguide QED 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.

What you will learn: Planning and designing of advanced projects with ultra-high vacuum systems, creative CAD construction, finite element simulations, advanced hands on optics skills, and cool physics!

  • To be announced
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Current vacuum glass cell in the rubidium experiment.

Rydberg EIT in ultracold Yb atom

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.

What you will learn: Advanced and high power optics, fiber optics, AOMs, optical traps, high voltage electronics, interfacing several hardware with control software, fast electronics and Data analysis.

  • To be announced
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Ultracold ytterbium in magneto-optical trap.

Single photon interferometer

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.

What you will learn: Quantum nature of photons, single photon detection, photon statistics, phase interferometry, fiber optics, AOM, fast electronics and data analysis

Probe and control setup
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Schematic drawing of probe scheming for ytterbium

Ultracold Rydberg atoms and integrated photonics in a cryostat

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.

What you will learn: set-up of fiber-optic experiments, numerical and experimental investigation of mechanical resonators, vacuum experiment techniques

Design proposal for the new cryogenic cold atom setup.

Magnetic trapping of ultracold atoms on a superconducting chip

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.

What you will learn: Laser cooling and magnetic trapping of atoms, advanced optics skills, numerical simulations, finite element simulations, electronics.

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First simulation of magnetic fields and potentials during the transfer of atoms between different traps.

Experiment control software for state-of-the-art quantum optics experiments

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.

What you will learn: Developing & optimizing complex hardware/software interface and GUI, design concepts of complex experiment control setups, working on large-scale software projects, …and some experimental atomic & optical physics…

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The computer control is looking for YOU!

Shaping optical potentials for single atoms and Rydberg superatoms

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 - socalled Rydberg Superatoms.

Very flexible optical dipole traps can be with for instance a Spatial Light Modulator (SLM). An SLM consists of a liquid crystal surface, which depending on an applied voltage alters the phase of a reflected laser beam. The different phases in the beam creates a holographic intensity pattern which can be used for a number of different applications, amongst others optical traps. This project focuses on the realization of such holographic traps with an SLM. Your task will be to design and build a testing setup to characterize the SLM itself, and the optical traps which can be realized with it, and then to implement your SLM-setup in the existing experiment.

What you will learn: Designing and building advanced optics setups, software-hardware interfacing, cool physics, thinking in Fourier space

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© NQO

Ultracold rubidium atoms in optical trapping potentials

Imaging of single photons

In quantum optics photon-photon correlations are crucial to distinguish between classical and non-classical light and to characterize quantum states of light. Usually, correlation measurements are done with single photon counters, which can reveal time-correlations between photons, but which do not offer any information about spatial correlations between photons. Spatial detection of individual photons is instead possible with electron multiplying CCD-cameras (EMCCD).

The main focus of this project is to set up and test a commercial EMCCD camera, in particular with correlated photons from a parametric down-conversion process, where a single high-energy photon is converted to two entangled photons of lower energy in nonlinear medium. If time allows it will also be your task to implement the EMCCD camera with the existing experiment and measure spatial correlations between photons which have been strongly coupled to Rydberg atoms.

What you will learn: Advanced optics, cool quantum concepts, designing and building experimental setups, software-hardware-interfacing

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Schematic drawing of camera setup

Preparation of ultracold Yb atoms

Yb atoms have interesting line structure which allows for exploration of exciting physics. Being a two electron system, Yb atoms offer a broad singlet and extremely narrow triplet transitions. The singlet transition, (6s2)1s0 to (6s6p)1p0 with a linewidth of ~28 MHz favours a high capture range for a magneto-optical trap (MOT). But due to the linewidth the MOT is limited to a high doppler temperature. The strongest triplet transition, (6s2)1s0 to (6s6p)3p1 on the other hand, is ~182 KHz broad with a doppler temperature of ~4uK. We utilize the two transitions for, first, loading a large number of atoms and then cooling them down to very low temperatures. Furthermore, the narrow transition is frequency swept repeatedly to increase phase-space density in a relatively new scheme called Sawtooth Wave Adiabatic Passage (SWAP) cooling.

Your task will be to realize the SWAP MOT scheme and optimize it. To explore the properties of the cold atoms you will set up a time-of-flight imaging. Your tasks will also involve the next step of optical trapping with an optical dipole trap.

What you will learn: Stabilization of laser frequencies, advanced optics, optical fibers, experiment control using software and hardware, interfacing various electronic devices and data analysis from the images of atom-cloud.

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© NQO

Ultracold ytterbium atoms

Interfacing Rydberg atoms with integrated photonic and RF circuits

The strong and long-ranged interactions between Rydberg atoms have been successfully used to mediate effective interactions between individual photons. Following demonstrations of e.g. single photon sources, optical transistors, or quantum gates in traditional ultracold atom setups, it is our goal to bring these closer to applications by implementing them “on-a-chip” with integrated photonic waveguides and to create interfaces between photons and superconducting RF circuits based on electromechanical oscillators.

In this project, you will be part of a team to build an unusual and innovative ultracold atom experiment. Atoms will initially be laser-cooled and trapped and then transported to a separate chamber where they can be interfaced with a variety of samples. You can contribute in a variety of ways, e.g. by designing and implementing magnetic traps for the atoms, electrode systems to manipulate Rydberg atoms with electric fields, or optical systems to excite and image the trapped atoms with lasers.

What you will learn: Using cryostats, ultra-high vacuum systems, laser cooling and trapping, advanced optics skills, CAD construction, finite element simulations.

Rendered drawing of possible experimental system.

Ultraprecise laser systems to create and manipulate Rydberg atoms

Interfacing ultracold Rydberg atoms with integrated photonic circuits requires laser light at well-defined optical frequencies to cool the atoms and excite them to Rydberg states. A key property of our hybrid-quantum systems is the coherence time of the different constituents. For Rydberg atoms, this is typically determined by the atomic state lifetime (µs to ms), and the frequency bandwidth of the laser light used to manipulate them. To maximise coherence times, it is therefore very important to reduce the laser linewidth to values comparable or below the natural linewidth of the Rydberg states.

In this project, you will set up laser systems required for both laser cooling and Rydberg excitation of the atoms. You will stabilise the frequency of the lasers to the resonances of an ultra-highfinesse (> 15000) optical resonator. Using the Pound-Drever-Hall technique, we aim for linewidths of order 100 Hz, corresponding to a precision of 10^-12 compared to the light’s frequency. You will get to work with both state-of-the-art lasers and a commercial optical resonator, which has been designed to experience almost no thermal drift when isolated from the environment in a vacuum-chamber to provide a stable frequency reference.

What you will learn: Advanced optics skills, high-precision laser frequency stabilisation, diode and frequency converted lasers, RF electronics, optimisation of fast feedback loops.

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© NQO

This laser will be part of the final ultrastable laser system!

Connectivity and Decoherence in Platforms for Quantum Computing and Simulation

Quantum many particle systems are spanning a Hilbert space which grows exponentially with the number of particles involved. To a large extent, it is this huge configuration space which holds the promise for the power of quantum computing and simulation through parallelism. Experimental platforms, on the other hand, have always limited access to this state space only.

This B.Sc. project aims at ordering and analyzing the interplay of connectivity (which and how many particles can be linked through interactions) and decoherence (the relaxation of quantum superposition states) for concrete physical platforms based on  screening and analyzing the literature.

What you will learn: This is a literature project for one or two bachelor students interested in obtaining an overview on current developments and challenges in the field of quantum technology. It will lay the groundwork for further theoretical and/or experimental work in your master studies.

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Scaling up qubits formed of Rydberg superatoms

Latest research news
Green ytterbium MOT

Green and shiny!

SuperWave

The project SuperWave has been awarded an ERC Synergy Grant!

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