Waveguide QED: controllable channel from quantum interference

TL;DR

This paper demonstrates how to create a controllable photon channel in waveguide QED systems using quantum interference, enabling perfect reflection or transmission without photon loss into other channels.

Contribution

It introduces the concept of a controllable channel (CC) in waveguide QED, achieved through multi-channel interference and Fano resonance, allowing lossless photon control.

Findings

The CC can be perfectly reflected or transmitted by the TLS.

Photon loss into other channels can be eliminated using the CC.

Dark states emerge with scattering-free channels orthogonal to CC.

Abstract

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