A bosonic topological phase in a paired superfluid

TL;DR

This paper investigates a topological phase in a two-species bosonic system, revealing a paired superfluid protected by symmetry, characterized by a novel bulk response and fractional vortices, with implications for cold atom experiments.

Contribution

It introduces a sign problem free Monte Carlo model of a topological paired superfluid in two dimensions with a new bulk response diagnostic.

Findings

Identification of a topological paired superfluid phase.

Introduction of an Ising-like quantized Hall response.

Observation of fractionally charged vortices.

Abstract

We study an effective model of two interacting species of bosons in two dimensions, which is amenable to sign problem free Monte Carlo simulations. In addition to conventional ground states, we access a paired superfluid which is also a topological phase, protected by the remaining $U(1) \times \mathbb{Z}_2$ symmetry. This phase arises from the condensation of a composite object, the bound state of vortices and anti-vortices of one species, to a boson of the second species. We introduce a bulk response function, the Ising analog of the quantized Hall effect, to diagnose the topological phase. The interplay of broken symmetry and topology leads to interesting effects such as fractionally charged vortices in the paired superfluid. Possible extensions towards realistic models of cold atomic bosons are discussed.