Observation of arbitrary topological windings of a non-Hermitian band

TL;DR

This paper experimentally demonstrates the non-trivial topological winding of energy bands in non-Hermitian systems using a modulated ring resonator, revealing controllable topological phases in non-conservative systems.

Contribution

It provides the first direct experimental observation of arbitrary topological windings in non-Hermitian band structures using a synthetic frequency dimension.

Findings

Direct measurement of complex band structures showing non-trivial winding

Control of topological winding via modulation waveform

Pathway for synthesizing topologically non-trivial phases in non-conservative systems

Abstract

The non-trivial topological features in the energy band of non-Hermitian systems provide promising pathways to achieve robust physical behaviors in classical or quantum open systems. A key topological feature, unique to non-Hermitian systems, is the non-trivial winding of the energy band in the complex energy plane. Here we provide direct experimental demonstrations of such non-trivial winding, by implementing non-Hermitian lattice Hamiltonians along a frequency synthetic dimension formed in a ring resonator undergoing simultaneous phase and amplitude modulations, and by directly characterizing the complex band structures. Moreover, we show that the topological winding can be straightforwardly controlled by changing the modulation waveform. Our results open a pathway for the experimental synthesis and characterization of topologically non-trivial phases in non-conservative systems.