Exact Quantum Many-Body Scar States in the Rydberg-Blockaded Atom Chain

TL;DR

This paper discovers exact quantum many-body scar states in a Rydberg atom chain, demonstrating violation of thermalization and explaining experimental oscillations through quasiparticle excitations.

Contribution

It explicitly constructs exact eigenstates at infinite temperature as matrix product states, revealing novel scar states and their role in nonthermal dynamics.

Findings

Exact eigenstates at infinite temperature found as matrix product states

Violation of strong eigenstate thermalization hypothesis demonstrated

Quasiparticle excitations explain experimental oscillations

Abstract

A recent experiment in the Rydberg atom chain observed unusual oscillatory quench dynamics with a charge density wave initial state, and theoretical works identified a set of many-body "scar states" showing nonthermal behavior in the Hamiltonian as potentially responsible for the atypical dynamics. In the same nonintegrable Hamiltonian, we discover several eigenstates at \emph{infinite temperature} that can be represented exactly as matrix product states with finite bond dimension, for both periodic boundary conditions (two exact $E = 0$ states) and open boundary conditions (two $E = 0$ states and one each $E = \pm \sqrt{2}$). This discovery explicitly demonstrates violation of strong eigenstate thermalization hypothesis in this model and uncovers exact quantum many-body scar states. These states show signatures of translational symmetry breaking with period-2 bond-centered pattern, despite being in one dimension at infinite temperature. We show that the nearby many-body scar states can be well approximated as "quasiparticle excitations" on top of our exact $E = 0$ scar states, and propose a quasiparticle explanation of the strong oscillations observed in experiments.