Tuning Topological Charge and Gauge Field Anisotropy in a Spin-1 Synthetic Monopole

TL;DR

This paper experimentally realizes a synthetic monopole in a spin-1 ultracold ensemble, demonstrating control over topological charge and anisotropy, and observing a topological phase transition with robustness under deformation.

Contribution

It introduces tunable spin-tensor coupling to engineer anisotropy and topological phases in a synthetic monopole system, advancing quantum simulation capabilities.

Findings

Measured the Chern number directly

Observed a topological phase transition

Verified robustness of topological charge

Abstract

Higher-dimensional Hilbert spaces in quantum simulation, as in all quantum science, expand the range of accessible phenomena. In this work, we experimentally realize a synthetic monopole using an ultracold spin-1 ensemble, where the monopole charge is quantified by the topologically invariant first Chern number and sources a synthetic magnetic field quantified by the Berry curvature. By using a three-level system with tunable spin-tensor coupling, we introduce anisotropy to the field, directly measure the Chern number, and observe a topological phase transition. We verify the robustness of the monopole's topological charge under deformation, and observe signatures of the topological phases using spin-texture and Majorana-star measurements. This work demonstrates spin-tensor coupling as a tuning parameter for engineering both geometric anisotropy and a rich topological phase space.