Abstract

Bose-Einstein condensates exhibit fascinating behavior such as super uidity and vortex formation, effects owing their presence to self-interactions between the underlying bosons [1]. In exciton-polariton condensates another peculiar effect has been theoretically predicted, where the negative energy Bogoliubov dispersion becomes observable in the photoluminescence (PL) spectrum [2{5]. The effect originates from the anomalous mixing of creation and destruction operators of polaritons, which results in the creation of a Bogoliubov particle when the PL is observed. Here we directly observe the PL of the negative Bogoliubov dispersion branch for the rst time in a high density regime far above the exciton-polariton condensation threshold. The observation is made possible by strong coupling being maintained at densities corresponding to 100 times the threshold density for condensation. The presence of strong coupling at such densities is evidenced by second-order coherence and PL measurements showing clear differences to photon lasing, a weak coupling phenomenon. Comparison of the negative dispersion PL spectrum shows good agreement to theoretical predictions.

© 2012 Optical Society of America