Controllable single-photon nonreciprocal propagation between two waveguides chirally coupled to a quantum emitter

We investigate coherent controlling single-photon nonreciprocal propagation in a pair of waveguides chirally coupled to an atom by using a classical optical field. The results show that for a nonresonant photon, the perfect single-photon nonreciprocal propagation can be realized by adjusting the Rabi frequency and detuning. Furthermore, the nonreciprocal propagation is switchable by using the classic field. The calculated results also show that the system can be used as a frequency filter to filter out some special frequencies for single-photon nonreciprocal propagation. The influences of nonperfect chiral coupling and dissipations on the nonreciprocal propagation are also shown.