Quantum many-body scars from virtual entangled pairs

TL;DR

This paper uncovers a new class of quantum many-body scars in a nonintegrable spin-1 XY model, characterized by exact eigenstates with area-law entanglement, leading to persistent revivals and weak ergodicity breaking.

Contribution

It introduces an analytical construction of quantum many-body scars via virtual entangled pairs, revealing their origin and entanglement structure in a nonintegrable system.

Findings

Exact, highly excited eigenstate with area-law entanglement constructed

Periodic revivals observed in quenched dynamics from specific initial states

Identification of entangled virtual spin-1/2 degrees of freedom underlying scars

Abstract

We study weak ergodicity breaking in a one-dimensional, nonintegrable spin-1 XY model. We construct for it an exact, highly excited eigenstate, which despite its large energy density, can be represented analytically by a finite bond-dimension matrix product state (MPS) with area-law entanglement. Upon a quench to a finite Zeeman field, the state undergoes periodic dynamics with perfect many-body revivals, in stark contrast to other generic initial states which instead rapidly thermalize. This dynamics can be completely understood in terms of the evolution of entangled virtual spin-1/2 degrees of freedom, which in turn underpin the presence of an extensive tower of strong-eigenstate thermalization hypothesis (ETH)-violating many-body eigenstates. The resulting quantum many-body scars are therefore of novel origin. Our results provide important analytical insights into the nature and entanglement structure of quantum many-body scars.