Exciton-polariton Bose-Einstein condensates (BEC) are a prime example of a macroscopic quantum state which emit coherent light over a large spatial region. Particularly, polariton BECs can be formed after non-resonant excitation above the threshold power with spontaneous formation of a macroscopic coherence in the lowest energy state.
We perform high temporal resolution second-order time correlation measurements performed on a CdTe microcavity where spontaneous Bose-Einstein condensation is observed. We can directly observe the nonresonantly excited thermal polariton population relax into a coherent polariton condensate by observing the g2(0) transition from 2 to 1. Following this very fast transition, we show that the emission possesses a very high coherence that persists for more than 100 ps after the build-up of the condensate.
Bose-Einstein condensation of exciton polaritons