Bose–Einstein condensation of polaritons is a growing field in semiconductor optics research, which exhibits spontaneous coherence similar to a laser, but through a different mechanism.
They therefore act like atoms which can approach equilibrium due to their collisions with each other, and can undergo Bose-Einstein condensation (BEC) at high density or low temperature.
Because the mechanism for the onset of coherence is the interactions between the polaritons, and not the optical gain that comes from inversion, the threshold density can be quite low.
Jaqueline Bloch and coworkers observed polariton condensation in 2009,[12] after which many other experimentalists reproduced the effect (for reviews see the bibliography).
The first clear demonstration of Bose–Einstein condensation of polaritons in equilibrium[15] was reported by a collaboration of David Snoke, Keith Nelson, and coworkers, using high quality structures fabricated by Loren Pfeiffer and Ken West at Princeton.