News
Periodic driving of a condensate reveals elementary excitations of photons coupled to a bath
A photon Bose–Einstein condensate (BEC) is a state of light in which photons occupy the ground state of an optical cavity when equilibrating with a material in thermal equilibrium — for example, molecules at room temperature. Due to the incoherent coupling between photons and molecules, the system exhibits new resonances, which can be linked to elementary excitations of the coupled system, which allow to gain deeper insight into the intricate link between coupling, drive and dissipation.
The Kennard-Stepanov relation has been verified for Xenon-Krypton mixtures
To realize a Bose-Einstein condensate of photons in the vacuum-ultraviolet regime (VUV), Xenon is a good candidate, provided its spectral lines are broadened by collisions using a second noble gas. We were able to show that Xenon provides promising transitions, whose upper state can be populated by two-photon transitions. We also were able to verify that the Kennard-Stepanov relation is fulfilled in a a Xeneon-Krypton mixture, a vital ingredient for the realization of a thermal photon gas.
Since 01.04.2025 Arif is an Assistant Professor at IIT
Our former postdoc at the erbium experiment, Arif Warsi Laskar was appointed Assistant Professor at the department of physics at the Indian Institute of Technology Guwahati in the region Assam. In the research group "Quantum Optics and Quantum Technology" he will use his experience gained in Bonn, and will, among others, set up experiments in gold gases.
Julian Schmitt has been appointed full professor at the Ruprecht-Karls University of Heidelberg
Julian will join the Kirchhoff-Institute for Physics as of 1st of January 2025 and the team members and labs will join the new laboratories in the next months of 2025. At Heidelberg, his experimental research group “Optical Quantum Systems” (optiQS) will explore emergent phenomena in quantum fluids of light, topological photonics and physical computation using open light-matter systems.
Kiran's paper on the 1d-2D crossover is published
It is long known that the dimensionality of a system has great influence on the laws of physics. In one dimension, the Hohenberg-Mermin-Wagner theorem predicts that, under some constraints, long-range order cannot be established in one dimension, as thermal fluctuations drive the system to an unordered situation. But what happens when going from two to one dimension? We have studied this crossover together with colleagues from the RPTU Kaiserslautern-Landau in a quantum gas of light.
Photons condense into a ring-like ground state
Photons confined in a potential with tunnel-coupled minima in a ring shape can populate the hybridized states of that ring. The ground state in such a ring is the symmetric superposition of the eigenstates of the individual wells, a smeared-out ringlike state. Using cooling enabled by thermal contact to a dye solution, we were able to coll directly into this ground state, and verify the phase coherence of the superposition state. The results have been published in Physical Review Letters.
Ultracold Rubidium atoms in lattices simulate strongly coupled systems
The quantum Rabi model describes the coupling of a two-level system to a bosonic mode, one prominent example is an atom coupled to a light field. When the coupling gets stronger than the relevant energy scales of the atom and the light field new effects are expected, for example a collapse ad revival of the initial state. In optical systems, however, this regime is not achievable, but cold atoms can simulate this regime. This proposal, conceived together with our theory colleagues from Bilbao, has been tested successfully in our lab.
Dr. Julian Schmitt receives the Wissenschaftspreis 2024 of the Industrie-Club Düsseldorf
Dr. Julian Schmitt from the Institute of Applied Physics received the Wissenschaftspreis 2024 of the Industrie-Club Düsseldorf for his groundbreaking research on quantum gases of photons, which on the one hand expand the understanding of quantum states in fundamental science and on the other hand can produce new technological components for the sensor technology or control of laser beams.
The quantum regression theorem has been verified for an optical quantum gas
A fundamental relation connecting the temporal fluctuations and the response behaviour has been experimentally observed in a quantum gas made of photons, the particles of light. The validity of this so-called quantum regression theorem could so far not be directly revealed for quantum gases.
Julian Schmitt awarded the Rudolf-Kaiser-Prize for Experimental Physics 2023
Dr. Julian Schmitt of the Institute for Applied Physics of the University of Bonn is awarded the Rudolf-Kaiser-Prize 2023 - one of the most renowned German prizes for young researchers in physics.
Thilo's paper on two-photon spectroscopy was published
An important step towards the realization of a VUV photon condensate has been achieved.
Our paper on Quantum Rabi-dynamics of trapped atoms far in the deep strong coupling regime published in Nat. Comm.
Our paper “Quantum Rabi dynamics of trapped atoms far in the deep strong coupling regime“ has been published in the journal Nature Communications. We report on a study of ultrastrong coupling between two mechanical modes of trapped cold atoms in the quantum Rabi regime. Using a novel experimental scheme, we achieve a Rabi coupling of 6.5 times the field mode frequency, so that the coupling term clearly dominates over all other energy scales for the first time.
Our paper on the fluctuation-dissipation theorem appears in PRL
The grand-canonical coupling of photons to a bath of dye molecules leads to fluctuations of the particle number. According to the fluctuation-dissipation theorem this is connected to a viscosity of the photon gas. In our experiment, we were able to prove the relation for a Bose-Einstein condesed gas for the first time.
Andreas Redmann takes part in the university Excellence Slam
Andreas Redmann presented his PhD project at the Excellence Slam of the university.
Media Coverage
Researchers of Bonn University have determined the compressibility of a quantum gas of light
[ Press release ][ Science Perspective article by R. Fletcher and M. Zwierlein ][ New Scientist article by A. Wilkins ][ Media Inaf article by V. Guglielmo ][ Physics World article by S. Jarman ]