Exciton-Polariton Condensate in a Ring Microcavity*

Ring microchannels for exciton-polaritons were created using optical photolithography followed by an inductively coupled plasma etch to pattern the top mirror of the microcavity in a ring shape. Due to the variation in the thickness of the microcavity across the ring, there was a gradient of potential energy across each ring. Polariton condensates were created by non-resonantly pumping the ring at the highest energy region using short laser pulses. A polariton condensate was formed at the location of the pump spot which flowed towards the minimum energy region. We observed natural oscillations of the condensate about this energy minimum by time resolving the photoluminescence using a streak camera. The time period of the oscillations was in good agreement with the numerical simulation of the time evolution of a wave packet in a rigid pendulum potential. A time-reversal -symmetry-broken rotational mode was also observed in the ring. The temporal oscillations in energy and density of the polaritons at a given spatial point provide a direct measurement of the exciton-exciton interaction strength (~ 5 μeV-μm²) in a GaAs quantum well.