Drift and Diffusion of Exciton-Polaritons in a Graded Quantum Microcavity

We report an experimental evidence of the acceleration of exciton–polaritons propagating in-plane of a semiconductor microcavity in the regime of the ballistic transport. The acceleration is achieved due to the gradient of the thickness of the cavity and results from the reciprocal space filtering effect of the cavity. The wave packet propagating in the cavity plane is constantly filtered by the cavity eigenmode that shifts towards larger wave vectors as the cavity width increases. The theory based on the extended scattering state technique reproduces the polariton transport in a graded cavity with a good accuracy.