Waveguide QED: Many-Body Bound State Effects on Coherent and Fock State Scattering from a Two-Level System

TL;DR

This paper investigates how many-body bound states in waveguide QED systems influence the scattering of Fock and coherent states, revealing significant non-Poissonian photon statistics at intermediate coupling strengths.

Contribution

It provides the exact many-body scattering eigenstates for a TLS coupled to a 1D bosonic continuum, highlighting the impact of multi-photon bound states on photon scattering.

Findings

Multi-photon bound states significantly alter scattering behavior.

Photon statistics become non-Poissonian with increased interaction strength.

One-photon probability decreases while multi-photon probabilities increase.

Abstract

Strong coupling between a two-level system (TLS) and bosonic modes produces dramatic quantum optics effects. We consider a one-dimensional continuum of bosons coupled to a single localized TLS, a system which may be realized in a variety of plasmonic, photonic, or electronic contexts. We present the exact many-body scattering eigenstate obtained by imposing open boundary conditions. Multi-photon bound states appear in the scattering of two or more photons due to the coupling between the photons and the TLS. Such bound states are shown to have a large effect on scattering of both Fock and coherent state wavepackets, especially in the intermediate coupling strength regime. We compare the statistics of the transmitted light with a coherent state having the same mean photon number: as the interaction strength increases, the one-photon probability is suppressed rapidly, and the two- and three-photon probabilities are greatly enhanced due to the many-body bound states. This results in non-Poissonian light.