Join us

We are very happy to welcome new group members!

On this page you find the open positions 222233and suggestions for student projects3443. If you want to hear more, do not hesitate to write an email to Sebastian Hofferberth.

To get an idea of what group-life looks like, check out our gallery page4554!2

PhD-students & PostDocs

We always have open positions for excellent PhD or Post Doc candidates. If you are interested in joining us, send your application, including CV, publications list and possible recommendations as a PDF file to Sebastian Hofferberth.

Student helper positions

We are always looking for enthusiastic students at any level (before and after the Bachelor thesis) who want to work in our lab. Topics include optics, electronics, or programming tasks. These jobs are a great opportunity to gain first lab work experience in parallel to your studies. If you are interested, just visit us and take a look at our lab or send us an email.

Bachelor- and Master-theses

We are offering Bachelor- and Master-projects for physics students. See the list of offered projects below or check it out here. 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 seen below, contact us via email or simply visit our labs.

Project ideas fall 2021

Optimization and higher order modes of polymer drum resonators

Cavity optomechanical experiments facilitate the interaction of light with mechanical resonators for example for force-sensing, wavelength conversion or for investigating many-body physics. The performance of these experiments crucially depends on the optimization of the involved mechanical resonators.

This project aims on the optimization of the mechanical properties of 3D laser-written polymer structures by exploring different types of vibrational modes and optimizing and re-designing the structure geometry using finite element simulations (COMSOL). A fiber cavity optomechanics experiment inside a vacuum chamber will be set up to test fabricated structures.

What you will learn: Finite-element simulations using COMSOL, set-up of fiber-optic experiments, vacuum experiment techniques

Little drum
Little drum © NQO

FEM-simulation of the fundamental flexural mode of a drum-type mechanical resonator

Double-tip fiber-cavity microscope for probing resonators arrays

Arrays of mechanical resonators can be probed via optical modes revealing how vibrational excitations are propagating in the system.

In this project an in-vacuum fiber-cavity microscope with two independently scannable fiber mirrors will be designed and set up in order to simultaneously couple to mechanical resonators. The mechanical resonators are 3D laser-written on a plane mirror substrate and can form chains and arrays of coupled membranes. The developed and fabricated structures will be investigated with the double tip fiber-cavity-microscope.

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


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

Holographic traps for 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



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


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 different MOT schemes and optimize them. To explore the properties of the cold atoms you will set up a time-of-flight imaging.

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.


Ultracold ytterbium atoms

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

Schematic drawing of probe scheming for ytterbium

Ultracold Rydberg atoms and integrated photonics in a cryostat

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 based on Rydberg interactions in traditional ultracold atom setups, it is our goal to bring these closer to practical applications by implementing them “on-a-chip” using integrated photonic waveguides. These require cooling to a few K to suppress thermal noise. A cryogenic environment also offers other benefits, like low blackbody radiation and reduced atom-surface interactions.

In this project, you will plan and build a rather unusual and innovative ultra-high vacuum system for experiments with cold atom ensembles in a cryogenic environment. You will design and build multiple interconnected vacuum chambers. Atoms will initially be laser-cooled and trapped atoms in a room temperature chamber and then transported to a cryogenic chamber. To reach just a few K, you will use a state-of-the-art closed-cycle cryostat, which, unlike older systems, no longer requires an external liquid helium supply.

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.


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