Experimental Characterization of Three-Band Braid Relations in Non-Hermitian Acoustic Systems

TL;DR

This paper experimentally investigates the complex three-band braid relations in non-Hermitian acoustic systems, revealing intricate topological behaviors and expanding understanding of non-Hermitian band topology.

Contribution

First experimental characterization of three-band braid relations in non-Hermitian acoustic systems using a novel cavity-tube structure with controllable unidirectional coupling.

Findings

Identification of noncommutative braid relations

Observation of swappable braid relations

Experimental reproduction of NH Bloch bands

Abstract

The nature of complex eigenenergy enables unique band topology to the non-Hermitian (NH) lattice systems. Recently, there has been a fast growing interest in the elusive winding and braiding topologies of the NH single and double bands, respectively. Here, we explore the even more intricate NH multi-band topology and present the first experimental characterization of the three-band braid relations by acoustic systems. Based on a concise tight-binding model, we design a ternary cavity-tube structure equipped with a highly controllable unidirectional coupler, through which the acoustic NH Bloch bands are experimentally reproduced in a synthetic dimension. We identify the NH three-band braid relations from both the perspectives of eigenvalues and eigenstates, including a noncommutative braid relation and a swappable braid relation. Our results could promote the understanding of NH Bloch band topology and pave the way toward designing new devices for manipulating acoustic states.