Exact Quantum Many-Body Scars in Higher-Spin Kinetically Constrained Models

TL;DR

This paper identifies exact quantum many-body scars in higher-spin kinetically constrained models, revealing new weak ergodicity breaking phenomena and broadening understanding of non-thermal states in complex quantum systems.

Contribution

It introduces a method to find exact many-body scars in higher-spin models, expanding the known classes of scar states beyond spin-1/2 systems.

Findings

Exact scars in higher-spin PXP models on arbitrary bipartite lattices.

Scar states in Fermi-Hubbard model with tilted potential as matrix product states.

Larger local degrees of freedom lead to more scar states and ergodicity breaking.

Abstract

We discover a variety of exact quantum many-body scars in higher-spin kinetically constrained models, through the recently developed DMRG-S algorithm [Zhang et al., Phys. Rev. Lett. 131, 020402]. Specifically, for the higher-spin PXP model on arbitrary bipartite lattices of any spatial dimension, we find exact many-body scars that are equidistantly spaced in the energy spectrum and exhibit similar structures to the ground state of the Affleck-Kennedy-Lieb-Tasaki model. For the one-dimensional Fermi-Hubbard model with a tilted potential in a certain parameter regime, whose effective model is equivalent to a kinetically constrained spin model with four degrees of freedom on each site, we find several many-body scars at energy $E=0$ and $E=\pm \sqrt{2}$ that can be exactly represented as matrix product states with finite bond dimensions. Our results demonstrate that larger local degrees of freedom in the kinetically constrained models provide a much broader space for the emergence of quantum many-body scars and weak ergodicity breaking.