# Collapse and revival of quantum many-body scars via Floquet engineering

## TL;DR

This paper demonstrates how periodic driving in a Rydberg atom chain can induce transitions between ergodic and non-ergodic quantum regimes, revealing a method to control quantum many-body scars and long-term coherence.

## Contribution

It introduces Floquet engineering as a tool to tune quantum many-body scars and ergodic behavior in a driven Rydberg system, showing reentrant transitions.

## Key findings

- Drive frequency controls ergodic and non-ergodic regimes.
- Floquet spectrum contains scars in non-ergodic regime.
- Long-time coherence is linked to Floquet scars.

## Abstract

The presence of quantum scars, athermal eigenstates of a many-body Hamiltonian with finite energy density, leads to absence of ergodicity and long-time coherent dynamics in closed quantum systems starting from simple initial states. Such non-ergodic coherent dynamics, where the system does not explore its entire phase space, has been experimentally observed in a chain of ultracold Rydberg atoms. We show, via study of a periodically driven Rydberg chain, that the drive frequency acts as a tuning parameter for several reentrant transitions between ergodic and non-ergodic regimes. The former regime shows rapid thermalization of correlation functions and absence of scars in the spectrum of the system's Floquet Hamiltonian. The latter regime, in contrast, has scars in its Floquet spectrum which control the long-time coherent dynamics of correlation functions. Our results open a new possibility of drive frequency-induced tuning between ergodic and non-ergodic dynamics in experimentally realizable disorder-free quantum many-body systems.