Mainz 2017 – scientific programme

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SYDD: Symposium Driven-dissipative Quantum Systems

SYDD 1: Driven-Dissipative Quantum Systems

SYDD 1.4: Invited Talk

Monday, March 6, 2017, 16:00–16:30, P 1

Calorimetry of a Bose-Einstein-condensed photon gas — •Martin Weitz — Institut für Angewandte Physik, Universität Bonn, Wegelerstr. 8, 53115 Bonn, Germany

Bose-Einstein condensation has been observed with cold atomic gases, quasiparticles in solid state systems as polaritons, and more recently also with photons in a dye-filled microcavity. I will here report on recent measurements of my Bonn group determining the heat capacity of the photon gas in the dye-filled microcavity system. Thermalization of photons is achieved in a number-conserving way by repeated absorption re-emission cycles on the dye molecules, and the cavity mirrors provide both an effective photon mass and a confining potential. When the thermalization by absorption and re-emission is faster than the photon loss rate in the cavity, the photons accumulate at lower energy states above the cavity low-frequency cutoff, and the system finally thermalizes to a Bose-Einstein condensate of photons. On the other hand, for a small reabsorption with respect to the photon loss, the state remains laser-like. The measurements of the heat capacity were performed under the conditions of the thermalization being much faster than both photon loss and pumping. At the Bose-Einstein phase transition, the observed specific heat shows a cusp-like singularity, as in the λ-transition of liquid helium, illustrating critical behaviour of the photon gas.