Photon transport mediated by a trimer QED system with PT-symmetry

The photon transport in a pair of parallel waveguides mediated by a parity-time- (PT-) symmetric trimer QED system is investigated. We demonstrate that the transport behaviors of the incident photons transferring between different waveguides can be actively controlled by the PT symmetry. The efficiency of such photon transport can be tuned to be much larger than 100% when the optical gain is introduced, and the transfer intensity is robust against the weak coupling among the atom, the cavity modes, their corresponding coupling mismatch, as well as the atomic dissipation. Furthermore, we demonstrate that when the system is excited by two input fields, the relative phase of the two input signals can serve as a sensitive control parameter for manipulating the photon transport, and controllable directional amplification of the incident signal photons with a fixed frequency can be realized by modulating the relative phase. The obtained results can be useful for designing phase-dependent active nonreciprocal devices, i.e., a phase-sensitive directional amplifier.