Multiple quantum scar states and emergent slow-thermalization in the flat-band system

TL;DR

This paper explores quantum many-body scars in a flat-band system, demonstrating how perturbations create multiple scar states with slow thermalization and ETH violation, supported by numerical evidence.

Contribution

It introduces a method to construct multiple QMBSs in a flat-band model and studies their properties under perturbations, revealing new insights into slow thermalization and ETH violation.

Findings

Multiple QMBSs can be constructed from degenerate states in flat-band models.

Perturbations lift degeneracy, creating states with sub-volume entanglement entropy.

Perturbed states exhibit slow-thermalization and ETH violation.

Abstract

Quantum many-body scars (QMBS) appear in a flat-band model with interactions on the saw-tooth lattice. The flat-band model includes a compact support localized eigenstates, called compact localized state (CLS). Some characteristic many-body states can be constructed from the CLSs at a low-filling on the flat-band. These many-body states are degenerate. Starting with such degenerate states we concretely show how to construct multiple QMBSs with different eigenenergies embedded in the entire spectrum. If the degeneracy is lifted by introducing hopping modulation or weak perturbations, these states lifted by these ways can be viewed as multiple QMBSs. In this work, we focus on the study of the perturbation-induced QMBS. Perturbed states, which are connected to the exact QMBSs in the unperturbed limit, indicate common properties of conventional QMBS systems, that is, a subspace with sub-volume or area law scaling entanglement entropy, which indicates the violation of the strong eigenstate thermalization hypothesis (ETH). Also for a specific initial state, slow-thermalization dynamics appears. We numerically demonstrate these subjects. The flat-band model with interactions is a characteristic example in non-integrable systems with the violation of the strong ETH and the QMBS.