Photon condensation： A new paradigm for Bose-Einstein condensation

Bose-Einstein condensation is a state of matter known to be responsible for peculiar properties exhibited by superfluid Helium-4 and superconductors. Bose-Einstein condensate （BEC） in its pure form is realizable with alkali atoms under ultra-cold temperatures. In this paper, we review the experimental scheme that demonstrates the atomic Bose-Einstein condensate. We also elaborate on the theoretical framework for atomic Bose-Einstein condensation, which includes statistical mechan- ics and the Gross-Pitaevskii equation. As an extension, we discuss Bose-Einstein condensation of photons realized in a fluorescent dye filled optical microcavity. We analyze this phenomenon based on the generalized Planck＇s law in statistical mechanics. Further, a comparison is made between photon condensateand laser. We describe how photon condensate may be a possible alternative for lasers since it does not require an energy consuming population inversion process.