Dynamical spectra from one and two-photon Fock state pulses exciting a single chiral qubit in a waveguide

TL;DR

This paper investigates the dynamical emission spectra of few-photon Fock states interacting with a chiral qubit in a waveguide, revealing nonlinear effects and the breakdown of weak excitation approximations.

Contribution

It provides analytical and numerical analysis of 1- and 2-photon excitation dynamics, highlighting nonlinear saturation and spectral effects in waveguide-QED.

Findings

Long-time spectrum matches input for 1-photon pulses

Rich population effects influence dynamical spectra

2-photon excitation shows nonlinear saturation signatures

Abstract

We study the dynamical light emission from few-photon Fock states in waveguide-QED with a chiral two-level system. We first investigate the time dynamics of the system by calculating the emitter population and illustrate the breakdown of the weak excitation approximation, for both 1-photon and 2-photon excitation. We show how a 1-photon pulse yields a transmitted long-time spectrum that is identical to the input pulse, despite significant population effects. However, the dynamical spectra and spectral intensity show rich population effects. We also show the differences between 1-photon and 2-photon excitation, where the latter shows clear signatures of nonlinear saturation effects. Analytical and numerically exact matrix product state solutions are shown.