Persistent, controllable circulation of a polariton ring condensate*

Exciton-polaritons are bosonic quasiparticles that are superpositions of excitons and photons. We report the direct observation of persistent circulation of a polariton ring condensate in a GaAs microcavity sample with no driving force and with no observable change in time.

A non-circulating ring condensate was prepared by an optical trap. The continuous-wave laser, modulated to a target-shape by SLM, not only generates polaritons but also creates a Mexican hat potential due to exciton-polariton interaction. The ring condensate was observed at the valley of potential. The circulation was initiated by a second, pulsed laser (probe), and the circulation direction was controlled by the probe position relative to high-density regions in the ring.

The phase of the circulating condensate was detected by taking the interference pattern of the ring condensate with its mirror image, and we monitored the phase change over time with a streak camera. A constant 2π phase jump along the ring was observed during the streak camera sweep time (2000ps), which is much longer than the polariton lifetime (~200ps) and pulse laser duration (~2ps). The 2π phase winding was also observed before and after the probe pulse, indicating the circulation persisted between the two laser pulses (14ns).

The theoretical analysis accurately simulated the experimental results. It reveals that the probe excites a vortex-antivortex pair, and only one vortex stays in the system, giving rise to the persistent circulation.