Temperature Dependence of Atomic Decay Rate

We investigate the decay rate of an atom in a two-dimensional optical microcavity in which there exists a Bose–Einstein condensation of photons. It is found that below the critical temperature T_c, the atomic decay rate depends on the absolute temperature T. Especially, at absolute zero temperature almost all photons are in the condensate state, and the atom can be approximately treated as if it is in vacuum.