Different Phases of Polariton Lasers

Nonequilibrium systems can exhibit new types of phase transitions not found in equilibrium ones, such as spontaneous pattern formation and phase separation. An interesting platform for studying such phenomena is the exciton-polaritons in semiconductor microcavities. As half-light half-matter quasi-particles, polaritons form an open, nonlinear system, which hosts the non-equilibrium counterpart of a rich variety of many-body phases. After a brief review of polariton condensation, we will discuss a few phenomena that bear unique signatures of non-equilibrium quantum phases, including limit cycle spontaneous oscillations of dissipatively coupled condensates, an electron-hole-photon Bardeen Cooper Schrieffer (BCS) state, and phase separation of dynamic Bose-Einstein condensate (BEC) and Berezinskii-Kosterlitz-Thouless (BKT) phases in a steady-state non-equilibrium polariton condensate