Single-photon scattering and bound states in an atom-waveguide system with two or multiple coupling points

TL;DR

This paper studies how single photons interact with a giant atom coupled at multiple points in a waveguide, revealing unique scattering behaviors, interference effects, and a phase transition in bound state formation.

Contribution

It introduces a detailed analysis of single-photon scattering and bound states in multi-coupling-point atom-waveguide systems, highlighting new interference effects and phase transition phenomena.

Findings

Single-photon reflection exhibits Breit-Wigner or Fano line shapes.

Destructive interference can lead to complete photon reflection.

A phase transition determines the existence of bound states based on coupling strength.

Abstract

In this paper, we investigate the single-photon scattering and bound states in a one-dimensional coupled-resonator waveguide which couples to a single artificial giant atom with two or more coupling points. When the atom couples to the waveguide via two resonators, the single-photon reflection rate is characterized by either Breit-Wigner or Fano line shapes. When the atom couples to the waveguide via multiple resonators, we numerically show how the destructive interference effect leads to a complete single-photon reflection. We also find a phase transition phenomena for the multi-resonator coupling case, which reveals that the upper bound state only exists when the atom-waveguide coupling strength is above a critical value.