Phase-modulated single-photon nonreciprocal transport and directional router in a waveguide-cavity-emitter system beyond the chiral coupling

We propose a potentially practical scheme for the controllable single-photon transport via waveguides which are coupled to a microcavity-emitter system. The microcavity-emitter system consists of a V-type three-level emitter and two or one single-mode microcavity. A driving field is used to drive a hyperfine transition between two upper excited states of the V-type three-level emitter. Beyond chiral coupling between waveguides and microcavity-emitter system, we show that the perfectly nonreciprocal single-photon transport in a single waveguide and the single-photon router with 100% routing probability in two waveguides can be achieved. Interesting enough, whether the nonreciprocal single-photon transport or the single-photon router can be switched periodically by adjusting the phase associated with microcavity-emitter coupling strength and the driving field. The complete physical explanation of the underlying mechanism is presented.