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Dynamics of an open photon Bose-Einstein condensate system


Martin Weitz, Frank Vewinger & Johann Kroha


Project B1 comprises an experimental and theoretical study of reservoir induced interactions between photons in a dye microcavity environment, where the dye molecules act as a tunable reservoir for photons trapped in the cavity. The thermal contact between photons and dye molecules generates two types of processes, (1) photon absorption and re-emission into the microcavity, allowing for thermalization of the photon gas, and (2) absorption and subsequent non-radiative decay of the dye molecule. The latter process leads to local heating and thus to local refractive index changes. Through this incoherent process the dye solution acts as a dynamically structured reservoir, imposing a thermooptic, temporally delayed effective photon-photon interaction on the photon gas, one of the central topics of this CRC. The dissipative interaction is expected to be responsible for novel effects on the quench dynamics of the photon gas.

The dye microcavity system is a prototype setup to study a system coupled to a dissipative reservoir, as it allows tuning from closed to open system dynamics. Bose-Einstein condensation of photons is observed when thermalization is faster than photon loss, while usual laser dynamics occurs for the opposite limit, where photons leave the cavity by mirror losses before thermalizing. In the dye microcavity, both the thermalization time and the loss rate can be tuned independently, and their interplay can be studied.

For atomic Bose-Einstein condensates, the dynamics after a sudden quench through the phase transition has been studied, and has been shown to follow the Kibble-Zurek scaling. In a photon Bose-Einstein condensate an additional timescale exists in the system, as the effective photon-photon interaction is dissipative and occurs temporally delayed. We will study the effect of these retarded system-reservoir interactions by investigating the formation of spontaneous vortices when performing sudden quenches through the Bose-Einstein phase transition, and test for possible deviations from the Kibble-Zurek scaling. In a second stage of the project, we plan to create effective magnetic fields for the optical quantum gas by time-periodic modulation of the trapping potential. In the two-dimensional quantum gas, this will lead to the formation of vortices, and will serve as a first step to reach the quantum Hall regime. Also in this regime the dye molecules act as a tunable reservoir for the photon gas, whose influence on the photon system will be investigated in detail in this joint theory-experimental project.

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