Waveguide quantum optomechanics: parity-time phase transitions in ultrastrong coupling regime

TL;DR

This paper presents a theoretical framework for waveguide quantum electrodynamics with mechanical qubit oscillations, revealing parity-time symmetry and phase transitions in the ultrastrong coupling regime, leading to observable subradiant states.

Contribution

It introduces a novel theoretical model predicting parity-time symmetry and phase transitions in waveguide QED systems with mechanical qubits in the ultrastrong coupling regime.

Findings

Prediction of parity-time symmetry in waveguide QED without engineered gain/loss

Identification of  phase transition leading to subradiant states

Feasibility of observing these phenomena in current experimental setups

Abstract

We develop a rigorous theoretical framework for interaction-induced phenomena in the waveguide quantum electrodynamics (QED) driven by mechanical oscillations of the qubits. Specifically, we predict that the simplest set-up of two qubits, harmonically trapped over an optical waveguide, enables the ultrastrong coupling regime of the quantum optomechanical interaction. Moreover, the combination of the inherent open nature of the system and the strong optomechanical coupling leads to emerging parity-time (\PT) symmetry, quite unexpected for a purely quantum system without artificially engineered gain and loss. The $\mathcal{PT}$ phase transition drives long-living subradiant states, observable in the state-of-the-art waveguide QED setups.