Topological Braiding of Bloch Eigenmodes Protected by Non-Abelian Quaternion Invariants

TL;DR

This paper introduces a novel form of topological braiding in non-Abelian topological insulators, demonstrating its realization in acoustic systems and highlighting its potential for robust classical and quantum wave applications.

Contribution

It proposes a new topological braiding mechanism based on non-Abelian quaternion invariants, extending topological protection to classical wave systems.

Findings

Braiding sequences are protected by non-Abelian band topology.

Experimental realization achieved in acoustic systems with synthetic dimensions.

Geometric phases are quantized over half the Brillouin zone.

Abstract

Braiding has attracted significant attention in physics because of its important role in describing the fundamental exchange of particles. Infusing the braiding with topological protection will make it robust against imperfections and perturbations, but such topological braiding is believed to be possible only in interacting quantum systems, e.g., topological superconductors. Here, we propose and demonstrate a new strategy of topological braiding that emerges from non-Abelian topological insulators, a class of recently discovered multi-band topological phase. We unveil a mathematical connection between braiding and non-Abelian quaternion invariants, by which Bloch eigenmodes under parallel transport produce braid sequences protected by the non-Abelian band topology. The braiding is also associated with geometric phases quantized over half the Brillouin zone. This new type of non-Abelian topological braiding is experimentally realized in acoustic systems with periodic synthetic dimensions. The results show that the principle discovered here is a new strategy towards topological braiding and can be extended for other types of classical waves and non-interacting quantum systems.