Strongly correlated photons with quantum feedback in a cascaded nanoscale double-cavity system

We characterize via the second-order correlation function the quantum correlations in the transmitted light in a two-cascaded-cavities system side-coupled to a common waveguide via bidirectional propagation. Adopting a full quantum master equation and standard input-output theory, we calculate the zero-time-delay second-order correlation function and identify clearly distinguished parameter regimes with the photon bunching and antibunching. Our numerical results clearly show that strong photon antibunching can be achieved in the cascaded double-cavity system without the need for extra modal-overlap-based coupling between the two cavities. Remarkably, this strong photon antibunching appears in the weak-coupling regime of cavity quantum electrodynamics. The photon antibunching properties can be manipulated by adjusting the propagation phase. In addition, we discuss the influences of the emitter-to-cavity coupling strength and the waveguide-to-cavity coupling rate on the photon antibunching. Also, the experimental feasibility of our proposal with the current photonic crystal technique is analyzed. This study offers an alternative way to generate the strongly antibunched photons, which may have applications in on-chip quantum information processing.