Quantum Trajectory Theory and Simulations of Nonlinear Spectra and Multi-Photon Effects in Waveguide-QED Systems with a Time-Delayed Coherent Feedback

TL;DR

This paper extends quantum trajectory simulations to study nonlinear spectra and multi-photon correlations in waveguide-QED systems with time-delayed feedback, revealing how feedback parameters influence photon statistics and introduce new resonances.

Contribution

It develops a quantum trajectory discretized-waveguide approach to analyze the effects of time-delayed feedback on nonlinear spectra and photon correlations in waveguide-QED systems.

Findings

Feedback can filter the Mollow triplet's central peak.

Proper phase choices switch photon output between bunched and anti-bunched.

Loop length and phase affect photon bunching and anti-bunching behaviors.

Abstract

We study the nonlinear spectra and multi-photon correlation functions for the waveguide output of a two-level system (including realistic dissipation channels) with a time-delayed coherent feedback. We compute these observables by extending a recent quantum trajectory discretized-waveguide (QTDW) approach which exploits quantum trajectory simulations and a collisional model for the waveguide to tractably simulate the dynamics. Following a description of the general technique, we show how to calculate the first and second order quantum correlation functions, in the presence of a coherent pumping field. With a short delay time, we show how feedback can be used to filter out the central peak of the Mollow triplet or switch the output between bunched and anti-bunched photons by proper choice of round trip phase. We further show how the loop length and round trip phase effects the zero-time second order quantum correlation function, an indicator of bunching or anti-bunching. New resonances introduced through the feedback loop are also shown through their appearance in the incoherent output spectrum from the waveguide. We explain these results in the context of the waiting time distributions of the system output and individual trajectories, uniquely stochastic observables that are easily accessible with the QTDW model.