Loop braiding statistics in exactly soluble 3D lattice models

TL;DR

This paper constructs two exactly solvable 3D lattice models to demonstrate the significance of three-loop braiding statistics in classifying gapped quantum phases, revealing their role in distinguishing different topological phases.

Contribution

The paper introduces two new exactly solvable 3D lattice models that explicitly demonstrate the role of three-loop braiding statistics in phase classification.

Findings

Different three-loop braiding phases indicate distinct quantum phases.

String and membrane operators effectively reveal braiding statistics.

Models support bosonic particle and loop excitations with nontrivial braiding.

Abstract

We construct two exactly soluble lattice spin models that demonstrate the importance of three-loop braiding statistics for the classification of 3D gapped quantum phases. The two models are superficially similar: both are gapped and both support particle-like and loop-like excitations similar to that of charges and vortex lines in a $\mathbb{Z}_2 \times \mathbb{Z}_2$ gauge theory. Furthermore, in both models the particle excitations are bosons, and in both models the particle and loop excitations have the same mutual braiding statistics. The difference between the two models is only apparent when one considers the recently proposed three-loop braiding process in which one loop is braided around another while both are linked to a third loop. We find that the statistical phase associated with this process is different in the two models, thus proving that they belong to two distinct phases. An important feature of this work is that we derive our results using a concrete approach: we construct string and membrane operators that create and move the particle and loop excitations and then we extract the braiding statistics from the commutation algebra of these operators.