Entanglement spectrum of a topological phase in one dimension

TL;DR

This paper demonstrates that the Haldane phase in one-dimensional S=1 chains exhibits a symmetry-protected double degeneracy in its entanglement spectrum, providing a scheme to classify gapped phases.

Contribution

It establishes that the degeneracy of the entanglement spectrum is protected by specific symmetries and can be used to classify topological phases in one-dimensional systems.

Findings

Double degeneracy of entanglement spectrum in Haldane phase

Degeneracy protected by certain symmetries

Scheme for classifying 1D gapped phases

Abstract

We show that the Haldane phase of S=1 chains is characterized by a double degeneracy of the entanglement spectrum. The degeneracy is protected by a set of symmetries (either the dihedral group of $\pi$-rotations about two orthogonal axes, time-reversal symmetry, or bond centered inversion symmetry), and cannot be lifted unless either a phase boundary to another, "topologically trivial", phase is crossed, or the symmetry is broken. More generally, these results offer a scheme to classify gapped phases of one dimensional systems. Physically, the degeneracy of the entanglement spectrum can be observed by adiabatically weakening a bond to zero, which leaves the two disconnected halves of the system in a finitely entangled state.