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Bose-Einstein Condensation of Light

Prof. Martin Weitz (University of Bonn)

Place: Salón de Grados
Time: 26.11.2015
Title: Bose-Einstein Condensation of Light

Bose-Einstein condensation, the macroscopic ground state accumulation of particles with integer spin (bosons) at low temperature and high density, has been observed in several physical systems, including cold atomic gases and solid state physics quasi-particles. However, the most omnipresent Bose gas, blackbody radiation, does not show this phase transition. The photon number here is not conserved (vanishing chemical potential), and at low temperatures photons disappear in the cavity walls instead of occupying the cavity ground state. Here I will describe an experiment observing Bose-Einstein condensation of photons in a dye-solution filled optical micro-cavity. The cavity mirrors provide a trapping potential and a non-vanishing effective photon mass, making the system formally equivalent to a two-dimensional gas of trapped massive bosons. Thermalization is reached in a number conserving way by repeated absorption re-emission cycles in the dye molecules. More recently, we have investigated the transition between usual lasing and photon Bose-Einstein condensation and also measured the coherence of the photon gas. In my talk, I will begin with a general introduction and give an account of current work and future plans of the Bonn photon gas experiment.