Angular topological superfluid and topological vortex in an ultracold Fermi gas

TL;DR

This paper demonstrates that an ultracold Fermi gas with spin-orbital-angular-momentum coupling can host topological superfluid phases and vortices, characterized by angular momentum space topology and Zak phase, with potential quantum information applications.

Contribution

It introduces a novel topological superfluid in ultracold Fermi gases with SOAMC, revealing a topological phase transition and stable topological vortex states in angular momentum space.

Findings

Identification of a topological phase transition via quasiparticle gap closing

Existence of a topological vortex state stabilized by Fermi surface deformation

Potential for experimental detection of topological phases and vortices

Abstract

We show that pairing in an ultracold Fermi gas under spin-orbital-angular-momentum coupling (SOAMC) can acquire topological characters encoded in the quantized angular degrees of freedom. The resulting topological superfluid is the angular analog of its counterpart in a one-dimensional Fermi gas with spin-orbit coupling, but characterized by a Zak phase defined in the angular-momentum space. Upon tuning the SOAMC parameters, a topological phase transition occurs, which is accompanied by the closing of the quasiparticle excitation gap. Remarkably, a topological vortex state can also be stabilized by deforming the Fermi surface, which is topologically non-trivial in both the coordinate and angular-momentum space, offering interesting potentials for applications in quantum information and quantum control. We discuss how the topological phase transition and the exotic vortex state can be detected experimentally.