Tuesday 4:30 pm (Freiburg) / 7:30 am (Vancouver)
(except for 14.10. and 21.10. On those days: 30 minutes later)

14.10.25 – Adrian Kirchner, TU Graz

04.11.25 – Grigorios Boulogiannis, Fraunhofer ISE Freiburg & Alexander Döring, University of Stuttgart

11.11.25 – Philipp Lunt, University of Heidelberg

18.11.25 – tba

25.11.25 – Info event for PhD students

02.12.25 – David Busto, Lund University, Sweden

09.12.25 – Workshop on „Choosing Career Paths after PhD“

16.12.26 – Patrick Rupprecht, Lawrence Berkeley National Laboratory, USA

13.01.26 – Federico Belli, Heriot-Watt University, UK

20.01.26 – tba

27.01.26 – Alexander Horn, Hochschule Mittweida, University of Applied Sciences

03.02.26 Johan Mauritsson, Lund University, Sweden

11.11.25 – Philipp Lunt, University of Heidelberg

Quantum Hall states with rotating atoms – a voyage into the vortex    

The fractional quantum Hall effect exhibits topologically ordered phases of matter resulting from the interplay of strong magnetic fields and interactions – many of which are famously described by Laughlin’s celebrated wavefunction. Ultracold neutral atoms in synthetic magnetic fields offer a promising platform to explore the microscopic origins of these states, thanks to their unparalleld control over interactions, as well as the manipulation and detection of individual particles.

Here, we showcase the realization of a Laughlin state with two rapidly rotating spinful fermions in an optical tweezer [1,2]. Utilizing our single-atom and spin-resolved imaging technique, we reveal its defining signature: suppression of inter-particle interactions due to a vortex distribution in the particles’ relative motion. Building upon this work, we extend our system to larger particle numbers, realizing a two-component integer quantum Hall (IQH) state comprised of three fermions in each spin state. This brings us in reach of studying the emergence of quantum phase transitions between IQH states of weakly interacting fermions and FQH states of interacting bosons, enabled via a Feshbach resonance to tune the inter-particles interactions [3].

[1] P. Lunt et al. Phys. Rev. Lett. 133, 25340 (2024)

[2] P. Lunt et al. Phys. Rev. A 110, 063315 (2024)

[3] G. Möller et al. PRL 99, 190409 (2007) 

Chair: Andreas Buchleitner

04.11.25 – Grigorios Boulogiannis, Fraunhofer ISE Freiburg & Alexander Döring, University of Stuttgart

Grigorios Boulogiannis:

Advancing Laser Processing Technology In Photovoltaics; Investigating the Linear and Nonlinear Optical Properties of Materials used in Photovoltaic Application

Laser processing plays a pivotal role in advancing materials used in the photovoltaic (PV) industry, aiming to improve efficiency, durability, and cost-effectiveness of solar technologies. Materials such as glasses, silicon carbide, and perovskites are of particular importance due to their optical, electrical, and structural properties. Ultrafast laser techniques enable precise modification of these materials through linear and nonlinear light–matter interactions, allowing for tailored surface and bulk functionalities. However, to fully harness the potential of such laser-based processes, a fundamental understanding of the linear and nonlinear optical absorption mechanisms governing these materials is essential. Gaining deeper insight into these interactions has the potential to facilitate the optimization of laser processing strategies and contribute to the development of next-generation photovoltaic devices.

Chair: Jale Schneider & Giuseppe Sansone

Alexander Döring:

Correlation measurements and simulations of light emitted by hot vapor microcells

This thesis is part of ongoing work to create a single-photon source based on thermal rubidium vapor in a thin microcell. The fundamental idea behind this concept consists in confining the excitation volume to a region smaller than the Rydberg blockade of an excited atom. The commonly used way to characterize non-classical light fields, such as a single photon source, is to measure the statistics of the photon flux via correlation measurements. Under specific circumstances, experimental noise and jitter can distort the measured correlations.
For a detailed examination of these effects, a numerical tool that can produce time stamps of a photon stream obeying an arbitrary given g(2) correlation function is developed, and its capabilities and limitations are discussed. Furthermore, a fundamental simulation framework for the four-wave mixing (FWM) experiment is set up, therefore allowing the
direct measurement of the influence on the g(2) correlation function of applying arbitrary effects on the photon stream.
Since current correlation measurements in the examined pulsed FWM scheme show no evidence of anti-bunching, this thesis investigates possible root causes via simulation and spectroscopic studies.
With the aforementioned tools, the influence of timing and width of the correlation window chosen for each pulse is simulated. It is shown that while they can strongly distort results when measuring on steep pulse flanks in a jitter-prone setup, correlation windows spanning large parts of the pulse around its maximum intensity precisely lead to the expected statistics.
The spectroscopic analysis is centered around fluorescence measurements studying the population of the involved 40S and 32S Rydberg states which is essential for the Rydberg blockade enabling the single-photon source concept. Severe broadening of the 40S state likely stemming from cell wall interaction is shown and spectrally narrow and time evolving features are characterized for the 32S state. The bulk of measured fluorescence stems from a three-photon Raman-type transition and, while a Rydberg blockade effect is found, no signal can conclusively be attributed to a populated Rydberg state.

Chair: Tobias Schätz

14.10.25 – Adrian Kirchner, TU Graz

Adrian Kirchner:

Generating short pulses at MHz repetition rates: Tabletop coherent radiation sources from the UV to the NIR

Chair: Lukas Bruder