Topologically Protected Exceptional Points and Reentrant $\mathcal{PT}$ Phase in an Exact Ternary Model

TL;DR

This paper introduces a minimal analytical model for open, driven systems with parity-time symmetry, revealing complex phenomena like reentrant phases and higher-order exceptional points, with potential applications in photonics and sensing.

Contribution

The paper presents a simple, exact model that unifies various phenomena in higher-dimensional PT-symmetric systems, including reentrant phases and topological exceptional points.

Findings

Identification of a new topological index underlying phenomena

Analytical solutions for higher-order exceptional points

Potential for experimental realization in photonics

Abstract

In open, driven systems where parity-time symmetry is preserved, phenomena that defy conventional wisdom emerge near exceptional points, promising advances in photonics. While most studies focus on two-level systems of a conventional exceptional point, unconventional exceptional points as well as reentrant phases have been discovered in separate studies of higher-dimensional phase spaces. In this Letter, we present a minimal, analytical model that encompasses several key phenomena in higher-dimensional phase spaces, including reentrant PT phases, higher-order exceptional points, and anisotropic exceptional points. Using the exact analytical solution, we identify a new topological index as the unifying origin of these different phenomena. The simplicity of the model may furthermore facilitate experimental implementations for enhanced sensing and efficient polariton devices.