# Mainz 2017 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 38: Quantum Gases: Bosons V

### Q 38.8: Vortrag

### Mittwoch, 8. März 2017, 16:15–16:30, P 204

**Fluctuation-dissipation relations in a Bose-Einstein condensed photon gas coupled to a dye reservoir** — •Fahri Emre Ozturk, Tobias Damm, David Dung, Frank Vewinger, Julian Schmitt, and Martin Weitz — Institut für Angewandte Physik, Universität Bonn, Wegelerstraße 8, 53115 Bonn, Germany

Bose-Einstein condensation, the phase transition of bosons to a macroscopically occupied ground state at low temperature, has been observed e.g. in cold atomic gases and semiconductor exciton-polaritons. We have previously observed Bose-Einstein condensation of a two dimensional photon gas in a dye filled optical microcavity [1]. The photon condensate shows grand canonical statistical behavior as the condensate exchanges both energy and particles with the dye reservoir. This results in photon number fluctuations, which can be as large as the average condensate photon number [2]. In thermal equilibrium, such fluctuations are related to the linear response of the system to a weak perturbation and thermal energy *k*_{B}*T*. This relation, expressed by the fluctuation-dissipation theorem, also explains e.g. the Brownian motion of suspended microscopic particles. Fluctuation-dissipation relations based on particle number fluctuations have not been studied previously in Bose-Einstein condensates. Here, we report on the status of current experimental work aiming at a study of the fluctuation-dissipation theorem for a condensed photon gas coupled to a dye reservoir.

[1] Klaers et al., *Nature* **468**, 545 (2010)

[2] Schmitt et. al., *Phys. Rev. Lett.* **112**, 030401 (2014)