Recent experiments have observed the Bose-Einstein condensation of photons. Confining the light in a multimode cavity along with a small amount of fluorescent dye allows it to thermalise to the temperature of the dye, undergoing a transition to a BEC above a critical pump strength. We have been involved with developing a microscopic model of this process allowing us to understand the thermalisation process in detail along with being able to predict many details of the experiments.
Recent publications about photon BEC are below:
Polarization dynamics in a photon Bose-Einstein condensate Ryan I. Moodie, Peter Kirton, and Jonathan Keeling Phys. Rev. A 96, 043844 (2017) arXiv
Spatial dynamics, thermalization, and gain clamping in a photon condensate Jonathan Keeling and Peter Kirton Phys. Rev. A 93, 013829 (2016) arXiv
Thermalization and breakdown of thermalization in photon condensates Peter Kirton and Jonathan Keeling Phys. Rev. A 91, 033826 (2015) arXiv
Nonequilibrium Model of Photon Condensation Peter Kirton and Jonathan Keeling Phys. Rev. Lett. 111, 100404 (2013) arXiv