Single-photon blockade in quasichiral atom-photon interaction: Simultaneous high purity and high efficiency

We investigate the single-photon blockade (1PB) in the quasichiral regime of atom-photon interaction that mediates via dissipative environment, where the effective atom-photon interaction is asymmetrical but achiral. The synthetic magnetic current in the closed-loop coupling breaks down the reciprocity of atom-photon interaction, resulting in an asymmetrical and even completely unidirectional effective coupling between two selected quantum states. As an example, we couple the single-atom cavity-QED (cQED) system to a strongly dissipative auxiliary cavity. We find that in the quasichiral regime, the unconventional photon blockade (UPB) always incorporates with the conventional photon blockade (CPB) in the condition of maximum chirality. Furthermore, we show that 1PB in the quasichiral regime combines the advantages of UPB and CPB, demonstrating the perfect single-photon purity, higher efficiency, smooth time dynamics as well as lower requirement of modes coupling to achieve UPB. Our work paves the way for 1PB towards practical applications and reveals the intriguing quantum-optics phenomena in the quasichiral light-matter interaction.