Polariton ring condensates and sunflower ripples in an expanding quantum liquid

Optically pumping high-quality semiconductor microcavities allows the spontaneous formation of polariton condensates, which can propagate over distances of many microns. Tightly focused pump spots here are found to produce expanding incoherent bottleneck polaritons, which coherently amplify the ballistic polaritons and lead to the formation of unusual ring condensates in space. This quantum liquid is found to form a remarkable sunflowerlike spatial ripple pattern, which arises from self-interference with Rayleigh-scattered coherent polariton waves in the {C} {C}{}erenkov regime.