Many-body physics of a quantum fluid of exciton-polaritons in a   semiconductor microcavity
  Some recent results concerning nonlinear optics in semiconductor microcavities are reviewed from the point of view of the many-body physics of an interacting photon gas. Analogies with systems of cold atoms at thermal equilibrium are drawn, and the peculiar behaviours due to the non-equilibrium regime pointed out. The richness of the predicted behaviours shows the potentialities of optical systems for the study of the physics of quantum fluids. 
Iacopo Carusotto, Michiel Wouters, Cristiano Ciuti