On the condensation of polaritons

Bose-Einstein condensates (BECs), the "fifth state of matter," have in fact been discovered by chance both in liquid helium and in superconductors. Since these early encounters, BECs have been sought for, both in atom vapors and in solids. Here we report on the case of exciton polaritons. We discuss the experimental observation of macroscopically occupied polariton states and their possible attribution to a BEC. We also discuss the possible relation between a polariton condensate, a polariton laser, and a vertical surface-emitting laser (VCSEL). Vortices, superfluidity, Bogoliubov dispersion, half-vortices, and Josephson oscillations are then briefly summarized merrily for sake of discussion of the distinction between a polariton BEC and a VCSEL. (C) 2012 Optical Society of America