Tunable Floquet selection rules in a driven Ising chain

TL;DR

This paper investigates a driven Ising chain and uncovers a Floquet selection rule that leads to novel prethermal phenomena such as Hilbert space fragmentation, Floquet freezing, and edge memory, with implications for Floquet engineering.

Contribution

It identifies a single Floquet selection rule that governs prethermal dynamics and leads to exotic phenomena like Hilbert space fragmentation and Floquet freezing in a driven Ising chain.

Findings

Hilbert space fragmentation emerges due to the Floquet selection rule.

Floquet freezing occurs at specific parameter ratios, suppressing spin flips.

Long-lived prethermal edge memory is observed without topological origin.

Abstract

We study a periodically driven spin-$1/2$ Ising chain with a nearest-neighbour coupling and longitudinal field while a weak transverse field induces single-spin flips. Through Floquet perturbation theory (FPT), we obtain signatures of Hilbert space fragmentation (HSF) and an unconventional form of dynamical localisation which we call the Floquet freezing. Our analysis suggests that these observations emerge due to a single Floquet selection rule that dictates the prethermal dynamics. For a special value of the field-to-interaction strength ratio together with commensurate drive periods, this rule permits only a constrained subset of bulk spin flips, leading to prethermal HSF in the full spin-$1/2$ Hilbert space. Under open boundary conditions, the same rule suppresses boundary spin flips up to higher order in perturbation and produces long-lived prethermal edge memory, which is neither topological in origin nor is a strong zero mode. Furthermore, under periodic boundary conditions, the largest surviving fragment is exactly the PXP sector at leading order and therefore exhibits Floquet-inherited scar phenomenology in the prethermal window. At higher commensurate ratios of field strength to interaction strength, all first-order single-spin-flip channels are suppressed and the system enters a regime of Floquet freezing. Hence, our study leverages the selection rules obtained through Floquet perturbation theory to obtain exotic prethermal phenomena at different parameter regimes.