Identifying quantum phases from injectivity of symmetric matrix product states

TL;DR

This paper introduces a method to classify quantum phases in one-dimensional systems with symmetry by analyzing the injectivity of symmetric matrix product states, avoiding traditional order parameters.

Contribution

It presents a novel approach to identify quantum phases using MPS injectivity and symmetry representations, applicable to various symmetries without local order parameters.

Findings

Successfully distinguishes symmetry-broken and symmetry-protected phases

Applicable to Hamiltonians with SO(3), Z_2, and Z_2 x Z_2 symmetries

Demonstrates effectiveness on translation invariant models

Abstract

Given a local gapped Hamiltonian with a global symmetry on a one dimensional lattice we describe a method to identify if the Hamiltonian belongs to a quantum phase in which the symmetry is spontaneously broken in the ground states or to a specific symmetry protected phase, without using local or string order parameters. We obtain different matrix product state (MPS) descriptions of the symmetric ground state(s) of the Hamiltonian by restricting the MPS matrices to transform under different projective representations of the symmetry. The phase of the Hamiltonian is identified by examining which MPS descriptions, if any, are injective, namely, whether the largest eigenvalue of the "transfer matrix" obtained from the MPS is unique. We demonstrate the method for translation invariant Hamiltonians with a global SO(3), Z_2 and Z_2 x Z_2 symmetry on an infinite chain.