We investigate an all-optical microscale planar lensing technique based on coherent fluids of semiconductor cavity exciton-polariton condensates. Our theoretical analysis underpins the potential in using state-of-the-art spatial light modulation of nonresonant excitation beams to guide and focus polariton condensates away from their pumping region. The nonresonant excitation profile generates an excitonic reservoir that blueshifts the polariton mode and provides gain, which can be spatially tailored into lens shapes at the microscale to refract condensate waves. We propose several different avenues in controlling the condensate fluid, and demonstrate formation of highly enhanced and localised condensates away from the pumped reservoirs. This opens new perspectives in guiding quantum fluids of light and generating polariton condensates that are shielded from detrimental reservoir dephasing effects.

Recent interest in the physics of non-perturbative light-matter coupling led to the development of solid-state cavity quantum electrodynamics setups in which the interaction energies are comparable with the bare ones. In such a regime the ground state of the coupled system becomes interactiondependent and is predicted to contain a population of virtual excitations which, notwithstanding having been object of many investigations, remain still unobserved. In this paper we investigate how virtual electronic excitations in quantum wells modify the ground-state charge distribution, and propose two methods to measure such a cavity-induced perturbation. The first approach we consider is based on spectroscopic mapping of the electronic population at a specific location in the quantum well using localised defect states. The second approach exploits instead the photonic equivalent of a Kelvin probe to measure the average change distribution across the quantum well. We find both effects observable with present-day or near-future technology. Our results thus provide a route toward a demonstration of cavity-induced modulation of ground-state electronic properties.