Topological Disorder Parameter

TL;DR

This paper introduces the topological disorder parameter (TDP), a new invariant for characterizing gapped quantum phases with symmetry, linking it to quantum dimensions and entanglement properties, and demonstrating its effectiveness through lattice models.

Contribution

The paper defines the TDP as a novel topological invariant, relates it to quantum dimensions and entanglement entropy, and applies it to various lattice models to detect topological order.

Findings

TDP scales as exp(-αl+γ) with γ related to quantum dimensions.

TDP reduces to topological Rényi entropy in certain symmetry cases.

Numerical and analytical results confirm TDP as a robust topological order detector.

Abstract

We introduce a many-body topological invariant, called the topological disorder parameter (TDP), to characterize gapped quantum phases with global internal symmetry in (2+1)d. TDP is defined as the constant correction that appears in the ground state expectation value of a partial symmetry transformation applied to a connected spatial region $M$, the absolute value of which scales generically as $\exp(-\alpha l+\gamma)$ where $l$ is the perimeter of $M$ and $\gamma$ is the TDP. Motivated by a topological quantum field theory interpretation of the operator, we show that $e^\gamma$ can be related to the quantum dimension of the symmetry defect, and provide a general formula for $\gamma$ when the entanglement Hamiltonian of the topological phase can be described by a (1+1)d conformal field theory (CFT). A special case of TDP is equivalent to the topological R\'enyi entanglement entropy when the symmetry is the cyclic permutation of the replica of the gapped phase. We then investigate several examples of lattice models of topological phases, both analytically and numerically, in particular when the assumption of having a CFT edge theory is not satisfied. We also consider an example of partial translation symmetry in Wen's plaquette model and show that the result can be understood using the edge CFT. Our results establish a new tool to detect quantum topological order.