Macroscopic Two-Dimensional Polariton Condensates
  We report a record-size, two-dimensional polariton condensate of a fraction of a millimeter radius free from the presence of an exciton reservoir. This macroscopically occupied state is formed by the ballistically expanding polariton flow that relaxes and condenses over a large area outside of the excitation spot. The density of this trap-free condensate is < 1 polariton/{\mu}m^2, reducing the phase noise induced by the interaction energy. Moreover, the backflow effect, recently predicted for the nonparabolic polariton dispersion, is observed here for the first time in the fast-expanding wave packet. 
Dario Ballarini, Davide Caputo, Carlos S\'anchez Mu\~noz, Milena De   Giorgi, Lorenzo Dominici, Marzena H. Szyma\'nska, Kenn...
cond-mat.quant-gas