A polariton laser. L. V. Butov in Nature 447:540 (2007). What the paper says!?
In this paper, L. Butov states that polariton coherence comes from it operating as a laser, not a BEC.
Commenting on S. Christopoulos et al.'s report of room temperature polariton condensation,[1] he asks a central question of polariton condensation and polariton lasing:
A coher ent state of electromagnetic waves is known as a laser; a coherent state of matter waves is termed a Bose–Einstein condensate. But what if a particle is a mixture of an electromagnetic wave and matter?
After citing the main literature to acknowledge cryogenic and (now) room-temperature coherent state:
So is this polariton coherent state similar to a laser, to a Bose–Einstein condensate, or some how to both? In other words, is it the electro magnetic-wave or the matter-wave component of the polariton that is responsible for establish ing the coherent state? This is an issue of more than semantic significance.
Butov's verdict:
The fundamentally different nature of a laser and a Bose–Einstein condensate is revealed in, for example, the different critical temperatures below which lasing or condensation occurs. Results so far show that the coherent states of micro cavity polaritons disappear when the photon component vanishes in a system of bare excitons, but remain strong when the exciton component vanishes in the weak-coupling regime. It seems that the coherence of the microcavity polaritons arises from the coher ence of an electromagnetic field — just as in a laser.
and then some polite concluding remarks on how this is is still interesting and useful for applications.