  Single-photon transport in non-ideal chiral photon-atom interaction
structures generally contains information backflow and thus limits the
capabilities to transfer information between distant emitters in cascaded
quantum networks. Here, in the non-ideal chiral case, a V -type atom coupled to
a waveguide is proposed to realize completely unidirectional transmission of
the single photons in a superposition state of different frequencies. A
microwave field is introduced to drive the two excited states of the atom and
results in photon conversion between two transitions. By adjusting the Rabi
frequency and the phase of the external driving field, the transport behaviors
of incident photons with specific frequencies can be optimized to complete
transmission or reflection. Based on the constructive interferences between
photons from different traveling paths, the transmission probabilities of the
specific-frequency photons could be enhanced. Due to photon conversions with
compensating the dissipations and ensuring the complete destructive
interference, the ideal unidirectional transmission contrast can be maintained
to 1, even when the atom has dissipations into the non-waveguide modes.
