Exciton-polariton Bose-Einstein condensation: advances and issues

In this review, we present a comprehensive set of experimental results on microcavity-polariton Bose-Einstein Condensation (BEC), obtained within a close collaboration between Institut Neel, Grenoble, France and EPFL, Lausanne, Switzerland. First, we recall the main observations, i.e., massive occupation of the ground state and build-up of long range order, which led us to conclude that polariton BEC indeed occurs. Then, the highly disordered environment in which the condensation takes place is considered: we show how interactions are a necessary ingredient for polariton BEC. Finally we discuss quantised vortices observed for the first time in polariton condensates. Their unusual features are shown to be inherited from the disordered environment and the driven-dissipative character of the polariton BEC.