Exact projected entangled pair ground states with topological Euler invariant

TL;DR

This paper introduces a new class of gapped PEPS with non-trivial Euler topology, representing a novel tensor network model for two-dimensional topological phases, including both free-fermionic and interacting states.

Contribution

It presents the first tensor network models of non-interacting, gapped 2D topological phases with Euler topology, and extends these models to interacting variants with characteristic entanglement features.

Findings

PEPS with non-trivial Euler topology constructed

Parent Hamiltonians with flat bands and unique ground states

Interacting variants share entanglement features with free states

Abstract

We report on a class of gapped projected entangled pair states (PEPS) with non-trivial Euler topology motivated by recent progress in band geometry. In the non-interacting limit, these systems have optimal conditions relating to saturation of quantum geometrical bounds, allowing for parent Hamiltonians whose lowest bands are completely flat and which have the PEPS as unique ground states. Protected by crystalline symmetries, these states evade restrictions on capturing tenfold-way topological features with gapped PEPS. These PEPS thus form the first tensor network representative of a non-interacting, gapped two-dimensional topological phase, similar to the Kitaev chain in one dimension. Using unitary circuits, we then formulate interacting variants of these PEPS and corresponding gapped parent Hamiltonians. We reveal characteristic entanglement features shared between the free-fermionic and interacting states with Euler topology. Our results hence provide a rich platform of PEPS models that have, unexpectedly, a finite topological invariant, forming the basis for new spin liquids, quantum Hall physics, and quantum information pursuits.