Observation of spin-tensor induced topological phase transitions of triply degenerate points with a trapped ion

TL;DR

This paper experimentally investigates topological phase transitions of triply degenerate points in a trapped ion system, revealing how spin-tensor--momentum couplings induce changes in topological charges through Berry flux measurements.

Contribution

It introduces a new method for measuring Berry flux via geometric rotations of spin vectors and tensors in a trapped ion platform, demonstrating topological phase transitions in high-spin systems.

Findings

Observation of topological charge jumps across phase transitions

Development of a generalized solid angle method for Berry flux measurement

Controlled simulation of high-spin topological phenomena in trapped ions

Abstract

Triply degenerate points (TDPs), which correspond to new types of topological semimetals, can support novel quasiparticles possessing effective integer spins while preserving Fermi statistics. Here by mapping the momentum space to the parameter space of a three-level system in a trapped ion, we experimentally explore the transitions between different types of TDPs driven by spin-tensor--momentum couplings. We observe the phase transitions between TDPs with different topological charges by measuring the Berry flux on a loop surrounding the gap-closing lines, and the jump of the Berry flux gives the jump of the topological charge (up to a $2\pi$ factor) across the transitions. For the Berry flux measurement, we employ a new method by examining the geometric rotations of both spin vectors and tensors, which lead to a generalized solid angle equal to the Berry flux. The controllability of multi-level ion offers a versatile platform to study high-spin physics and our work paves the way to explore novel topological phenomena therein.