Slow reflection and two-photon generation of microcavity exciton–polaritons

When photons in an optical cavity couple to a sharp electronic resonance, new states appear that are mixed states of photons and excitons, known as polaritons. The polaritons can be viewed as photons with an effective mass and with repulsive interactions. In the studies reported here, we have resonantly injected polaritons into a cavity and tracked them in time and space over millimeter distances as they experience a force due to a gradient of cavity width. Their motion is well described by the equations of motion for a moving mass under a constant force, that is, a parabolic trajectory. This can be called “slow reflection,” as the photons gradually decelerate, turn around, and go back the other direction. From these measurements we can accurately measure the lifetime of the polaritons in our samples to be 180 ± 10 ps, over 1 order of magnitude longer than previous works. This corresponds to a cavity leakage time of 135 ps and a cavity Q of 320,000. Additionally, we have shown the same effect with polaritons generated by direct two-photon excitation of the polariton states, allowing the possibility of modulation of two-photon absorption by a polariton condensate.