Periodic squeezing in a polariton Josephson junction

Microcavity polaritons are a hybrid photonic system that arises from the strong coupling of confined photons to quantum-well excitons. Due to their light-matter nature, polaritons possess a Kerr-like nonlinearity while being easily accessible by standard optical means. The ability to engineer confinement potentials in microcavities makes polaritons a very convenient system to study spatially localized bosonic populations, which might have great potential for the creation of novel photonic devices. Careful engineering of this system is predicted to induce Gaussian squeezing, a phenomenon that lies at a heart of the so-called unconventional photon blockade associated with single photon emission. This paper reveals a manifestation of the predicted squeezing by measuring the ultrafast time-dependent second-order correlation function g
⁽²⁾
(0) by means of a streak-camera acting as a single photon detector. The light emitted by the microcavity oscillates between Poissonian and super-Poissonian in phase with the Josephson dynamics. This behavior is remarkably well explained by quantum simulations, which predict such dynamical evolution of the squeezing parameters. The paper shows that a crucial prerequisite for squeezing is presence of a weak, but non-zero nonlinearity. Results open the way towards generation of nonclassical light in solid-state systems possessing a single particle nonlinearity like microwave Josephson junctions or silicon-on-chip resonators.