Exploring Non-Abelian Geometric Phases in Spin-1 Ultracold Atoms

TL;DR

This paper experimentally investigates non-Abelian geometric phases in spin-1 ultracold atoms, revealing richer topological properties and the significance of singular loops within the phase space, advancing understanding of topological quantum phenomena.

Contribution

It introduces an experimental exploration of non-Abelian geometric phases for singular loops in spin-1 systems using ultracold atoms, highlighting the complex topology of the phase space.

Findings

Observation of non-Abelian geometric phases in spin-1 atoms

Identification of the role of singular loops passing through the Bloch sphere center

Demonstration of the topological differences from spin-1/2 systems

Abstract

Non-Abelian and non-adiabatic variants of Berry's geometric phase have been pivotal in the recent advances in fault tolerant quantum computation gates, while Berry's phase itself is at the heart of the study of topological phases of matter. The geometrical and topological properties of the phase space of spin$-1$ quantum states is richer than that of spin$-1/2$ quantum states and is relatively unexplored. For instance, the spin vector of a spin-1 system, unlike that of a spin$-1/2$ system, can lie anywhere on or inside the Bloch sphere representing the phase space. Recently, a generalization of Berry's phase that encapsulates the topology of spin-1 quantum states has been formulated in J. Math. Phys., 59(6), 062105. This geometric phase includes loops that go inside the Bloch sphere and is carried by the tensor of spin fluctuations, unlike Berry's phase which is carried by the global phase of the quantum state. Furthermore, due to a mathematical singularity at the center of the Bloch sphere, the class of loops that pass through the center are called singular loops and are significant because their geometric phase is non-Abelian. In contrast with Berry's phase for spin$-1/2$ systems, whose properties come from the topology of a sphere, the properties of singular loop geometric phases come from the topology of the real projective plane $\mathbb{RP}^2$, which is more non-trivial. Here we use coherent control of ultracold $^{87}$Rb atoms in an optical trap to experimentally explore this geometric phase for singular loops in a spin-1 quantum system.