A Passive $\mathcal{PT}$-Symmetric Floquet-Coupler

TL;DR

This paper introduces a passive $ ext{PT}$-symmetric Floquet system in coupled optical waveguides with periodically modulated loss, demonstrating reduced loss requirements for symmetry breaking and potential reservoir engineering implementations.

Contribution

It presents a novel Liouville-space approach to model a passive $ ext{PT}$-symmetric Floquet system with modulated loss in coupled waveguides, highlighting resonance effects and physical implementation methods.

Findings

Resonance enhances $ ext{PT}$-symmetry breaking at lower loss levels.

Multi-photon states exhibit clear $ ext{PT}$ transition signatures.

Reservoir engineering can realize the modulated loss physically.

Abstract

Based on a Liouville-space formulation of open systems, we present a solution to the quantum master equation of two coupled optical waveguides with varying loss. The periodic modulation of the Markovian loss of one of them yields a passive $\mathcal{PT}$-symmetric Floquet system that, at resonance, shows a strong reduction of the required loss for the $\mathcal{PT}$ symmetry to be broken. We showcase this transition for a multi-photon state, and we show how to physically implement the modulated loss with reservoir engineering of a set of bath modes.