Emission spectral non-Markovianity in qubit-cavity systems in the ultrastrong coupling regime

TL;DR

This paper develops a polaron-transformed Nakajima-Zwanzig master equation to accurately compute emission spectra in non-Markovian, ultrastrong qubit-cavity systems, revealing asymmetries and the importance of counter-rotating terms.

Contribution

It introduces a novel PTNZE approach that overcomes limitations of traditional methods for modeling emission spectra in ultrastrong coupling regimes.

Findings

PTNZE accurately predicts emission spectra where standard methods fail.

Spectra are generally asymmetric under various initial conditions.

Counter-rotating terms significantly influence spectral features.

Abstract

We study the emission spectra of dissipative Rabi and Jaynes-Cummings models in the non-Markovian and ultrastrong coupling regimes. We have derived a polaron-transformed Nakajima-Zwanzig master equation (PTNZE) to calculate the emission spectra, which eliminates the well known limitations of the Markovian approximation and the standard second-order perturbation. Using the time-dependent variational approach as benchmark, the PTNZE is found to yield accurate emission spectra in certain ultrastrong coupling regimes where the standard second-order Nakajima-Zwanzig master equation breaks down. It is shown that the emission spectra of the dissipative Rabi and Jaynes-Cummings models are in general asymmetric under various initial conditions. Direct comparisons of spectra for the two models illustrate the essential role of the qubit-cavity counter-rotating term and the spectra features under different qubit-cavity coupling strengths and system initial conditions.