Superfluidity, closely related to Bose-Einstein condensation (BEC), exhibits quantum depletion even at zero temperature. This study observes quantum depletion in a high-density exciton-polariton condensate by analyzing the spectral branch of elementary excitations. Results show that quantum depletion can closely follow or deviate from equilibrium Bogoliubov theory depending on the exciton fraction, revealing beyond mean-field effects and highlighting the complex relationship between equilibrium and non-equilibrium BECs.

Maciej Pieczarka, Eliezer Estrecho, Maryam Boozarjmehr, Olivier Bleu, Mark Steger, Kenneth West, Loren N. Pfeiffer, David W. Snoke, Jesper Levinsen, Meera M. Parish, Andrew G. Truscott, Elena A. Ostrovskaya