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Antibunching effect of photons in a two-level emitter-cavity system

A two-level quantum emitter interacting with a cavity field is an important model for investigating the photon blockade (PB) effect. Most work on this topic relies on the assumption that the emitter transition frequency is resonant with the fundamental mode frequency of the cavity. In this work we relax this constraint and reexamine the PB effect in a more general emitter-cavity system with arbitrary emitter and cavity detunings from a driving field. The results show that when the signs of the emitter and cavity detunings are the same, a PB occurs only in the strong-coupling regime, but for opposite signs of the emitter and cavity detunings, strong photon antibunching is observed in both the weak- and strong-coupling regimes, and better antibunching is achieved compared with the case when the signs are the same. More interestingly, we find that this PB arises from quantum interference for both weak and strong nonlinearities. These results deepen our understanding of the underlying mechanism of PBs and may contribute to the construction of single-photon sources with higher purity and better flexibility using two-level emitter-cavity systems.