Coherence of the exciton condensate luminescence

A new experiment to detect Bose-Einstein condensation of excitons is suggested. The experiment is a photon-counting measurement of the exciton luminescence with two detectors. As a result, the number of photons N(t) and the second-order coherence $g^{(2)}(t)$ emitted during the time interval t can be obtained. These quantities contain contributions from both the normal component and the condensate. It is shown in the paper that the number of photons emitted by a condensate, $N^{(2)}(t)$, can be found from the expression $ [N^{(2)}(t) ]^{2}=2 [N(t) ]^{2}-g^{(2)}(t)$. The integration of $N^{(2)}(t)$ over the spectrum gives the value of the order parameter.