Probing dressed states and quantum nonlinearities in a strongly coupled three-qubit waveguide system under optical pumping

TL;DR

This paper investigates a three-qubit waveguide system under optical pumping, revealing complex dressed states and quantum nonlinearities, and compares Markovian and non-Markovian theoretical models to understand its spectral properties.

Contribution

It introduces a detailed analysis of a three-qubit waveguide system with strong coupling, highlighting nonlinear effects and limitations of Markovian approximations.

Findings

Rich manifold of dressed states observed in emitted spectrum

Nonlinear spectrum varies with decay rates and qubit separation

Markovian models have limitations in capturing system dynamics

Abstract

We study a three-qubit waveguide system in the presence of optical pumping, when the side qubits act as atomlike mirrors, manifesting in a strong light-matter coupling regime. The qubits are modelled as Fermionic two-level systems, where we account for important saturation effects and quantum nonlinearities. Optically pumping this system is shown to lead to a rich manifold of dressed states that can be seen in the emitted spectrum, and we show two different theoretical solutions using a medium-dependent master equation model in the Markovian limit, as well as using matrix product states without invoking any Markov approximations. We demonstrate how a rich nonlinear spectrum is obtained by varying the relative decay rates of the mirror qubits as well as their spatial separation, and show the limitations of using a Markovian master equation. Our model allows one to directly model giant-atom phenomena, including important retardation effects and multi-photon nonlinearities. We also show how the excited three qubit system, in a strong coupling regime, deviates significantly from a Jaynes-Cummings model when entering the nonlinear regime.