Stochastic precession of the polarization in a polariton laser

Microcavity polaritons in the lasing regime undergo a spontaneous symmetry breaking transition resulting in coherent emission with a well defined polarization. The order parameter is thus a vector describing both the laser global phase and polarization. Using an ultrafast single-shot detection technique we show that polariton lasing in GaAs-based microcavities presents a high degree of second order coherence ($g^{(2)}(\tau=0) \approx 1$) above threshold, and that the initial polarization is stochastic, taking any possible direction in the Poincar\'e sphere (linear, elliptical or circular). Once the polarization direction is established, subsequent oscillations of the emission probability witness the presence of an intrinsic polarization splitting. Our results show the negligible role of polariton interactions in the total emission statistics and in the establishment of the initial polarization.Comment: 9 pages, 6 figure