Partial Quantisation of Non-Hermitian Berry Phases in Time-Varying Media

TL;DR

This paper explores the topological properties of non-Hermitian wave systems in time-varying media, focusing on quantized Berry phases and their measurement in experimental setups.

Contribution

It provides explicit formulas for the topological index in practical non-Hermitian models, including an analogue of the Su-Schrieffer-Heeger model.

Findings

Berry phase's real part is quantized and measurable in experiments.

Topological index derived explicitly for specific non-Hermitian models.

Non-Hermitian topology can be characterized in time-varying media.

Abstract

A fundamental symmetry of the non-Hermitian operators describing wave-propagation in time-varying media imbue such systems with non-trivial topology. This topology may be measured directly in a wide range of experimental settings as a quantised real part of the Berry phase, contrasting unconstrained geometric gain or loss. This topological index is provided explicitly for practical examples, including a non-Hermitian analogue of the Su-Schrieffer-Heeger model.