QuantuM Optics correlations on a chip

cavity quantum electrodynamics describes the behaviour of a quantum emitter inside an optical cavity, and is one of the few realizable experimental systems in which the coherent interaction between the emitter and the cavity mode can exceed dissipative and dephasing processes. Recent advances in this field include the observation of vacuum Rabi splitting1–3, interference4, upconversion5 and the metasurface enhancement6 of single photons, as well as cavity–exciton photon blockade and tunnelling7 on a semiconductor chip. In addition, by varying the local density of optical states to control spontaneous emission, researchers have demonstrated highly efficient quantum dot single-photon sources with sub-Poissonian statistics8. Now, writing in Nature Photonics, Reinhard et al.9 report strong photon–photon quantum correlations on the first and second Jaynes–Cummings manifolds for a single quantum dot coupled to a photonic crystal nanocavity, even in the presence of quantum dot blinking. The behaviour of a two-level quantum emitter–cavity system is described by the Jaynes–Cummings standard model10,11, in which spontaneous emission can be controlled through coherent atom– vacuum field interactions. The quantum emitter–cavity system is described by the Rabi interaction rate g, the quantum emitter decoherence or decay rate γ, and the cavity photon decay rate κ. In the weak coupling regime, the emitter or the cavity photon decay rate is greater than the Rabi interaction rate. There is an irreversible energy exchange between the emitter and the cavity photon, with a Purcell-modified spontaneous emission rate that is based on the local density of states. In the strong coupling regime, the Rabi interaction rate exceeds the cavity or quantum emitter decay rate, with reversible spontaneous emission and multiple re-absorption/re-emission oscillations between the emitter and the cavity mode. The resulting strongly coupled open system exhibits the solid-state analogue of vacuum Rabi splitting with normal-mode splitting in the spectral domain, and is significantly perturbed by the detection event10, which collapses the wavefunction and causes the second-order correlation function at zero time delay, g(2)(0), to tend to zero. This is understood as the stochastic renormalization of the cavity emission rate after the first photon emission, which has strong photon antibunching character. The exciton–photon polariton energy ladder displays distinct anharmonicity. When probed on the second rung of the Jaynes–Cummings ladder, the strongly coupled polariton system can exhibit photon bunching, thereby providing optical nonlinearities at the few-photon level that QuantuM Optics