QSE Quantum Seminar: Compressibility and the equation of state of an optical quantum gas in a box

Please join us for the QSE Center Quantum Seminar with Dr. Julian Schmitt from University of Bonn, who will give the talk "Compressibility and the equation of state of an optical quantum gas in a box" on Thursday May 23.
Location: CM 1 221

Pizzas will be available before the seminar at 12:00. All PhDs, postdocs, students, and PIs are welcome to join us.

TITLE: Compressibility and the equation of state of an optical quantum gas in a box

ABSTRACT: Quantum gases of atoms, exciton-polaritons, and photons provide a test bed for many-body physics under both in- and out-of-equilibrium settings. Experimental control over their dimensionality, potential energy landscapes, or the coupling to reservoirs offers wide possibilities to explore phases of matter, for example, by probing susceptibilities, as the compressibility. For gases of material particles, such studies of the mechanical response are well established, in fields from classical thermodynamics to cold atomic quantum gases; for optical quantum gases, they have so far remained elusive.

In my talk, I will discuss experimental work demonstrating a measurement of the compressibility of a two-dimensional quantum gas of photons in a box potential, from which we obtain the equation of state for the optical medium. The experiment is carried out in a nanostructured dye-filled optical microcavity. We observe signatures of Bose-Einstein condensation at large phase-space densities in the finite-size system. Upon entering the quantum degenerate regime, the density response to an external force sharply increases, hinting at the peculiar prediction of a highly compressible Bose gas. In other recent work, we have demonstrated a test of the fluctuation-dissipation relation in photon Bose-Einstein condensates by independent measurements of the density response and the reservoir-induced grand canonical fluctuations.

BIO: Prof. Schmitt obtained a PhD in Physics from University of Bonn with a thesis on “Dynamics and correlations of a Bose-Einstein condensate of light”. He continued as a Postdoctoral researcher on "Experimental and theoretical work on correlations in optical quantum fluids and first demonstration of variable potentials for coupled condensates of light". Subsequently, he held positions as a Research Associate at Cavendish Laboratory where he focused on "Experimental work on ultracold-atom quantum gases in two dimensions", demonstrating “universal jump” of a topological BKT superfluid for the first time. Since 2020, he has been the University of Bonn Principal Investigator within SFB/TR 185 “Open System Control of Atomic and Photonic Matter” and Cluster of Excellence “Matter and Light for Quantum Computing” (ML4Q). He is now the Leader of ERC junior group ‘Quantum Fluids of Light’ and his research is centered on "Experimental work on complex lattice systems of photon Bose-Einstein condensates in contact to tailored environments, uniform optical quantum gases, and topological states in plasmon-polariton systems".