Waveguide quantum electrodynamics: Controllable channel from quantum interference

We study a waveguide QED system with a rectangular waveguide and a two-level system inside, where the transverse magnetic TMmn modes define the quantum channels of guided photons. It is discovered that the loss of photons from the TM11 channel into the others can be overcome by replacing it with a certain coherent superposition of TMmn channels, which is named the controllable channel (CC), as the photons in the CC can be perfectly reflected or transmitted by the two-level system and never lost into the other channels. A dark state emerges when the photon is incident from one of the scattering-free channels orthogonal to the CC. The underlying physics mechanism is the multichannel interference associated with Fano resonance.