Emergence of prethermal time quasicrystalline order in a quasiperiodically driven non-interacting spin chain

TL;DR

This paper demonstrates the emergence and stability of prethermal time quasicrystalline order in a quasiperiodically driven non-interacting spin chain, highlighting robustness against perturbations and potential for long-lived nonequilibrium temporal phases.

Contribution

It introduces a new quasiperiodically driven spin system exhibiting stable prethermal time quasicrystalline order with robustness comparable to discrete time crystals.

Findings

Spectral peaks at incommensurate frequencies indicate quasiperiodic time-translation symmetry breaking.

Entanglement entropy shows sublinear growth and a prethermal plateau, signifying suppressed heating.

System remains stable against NNN exchange and rotational imperfections, demonstrating robustness.

Abstract

We study prethermal time quasicrystalline (TQC) order in a quasiperiodically driven chain of non-interacting spin-1/2 particles. The drive consists of two parts, switched on and off periodically with frequency $\omega_d$: (i) disordered Ising interactions, with exchange couplings chosen from a symmetric interval $[-J/2, J/2]$, allowing random antiferromagnetic or ferromagnetic nearest-neighbor couplings, together with a random transverse field; and (ii) a rotating transverse magnetic field with frequency $\Omega$. The ratio $\omega_d/\Omega$ is chosen to be irrational, producing multiple incommensurate frequencies and yielding quasiperiodic dynamics beyond Floquet theory. Using exact diagonalization, we analyze the time autocorrelation function, dynamical structure factor, and entanglement entropy (EE). In the high-frequency regime, robust spectral peaks at incommensurate frequencies (not integer multiples of the fundamental drives) signal quasiperiodic time-translation symmetry breaking (QTTSB). The EE exhibits sublinear power-law growth followed by a prethermal plateau, indicating suppressed resonant heating due to an energy scale mismatch. The nonequilibrium lifetime increases rapidly with driving frequency. Unlike symmetric disorder sampling, an asymmetric distribution of the Ising exchange couplings induces collective spin rigidity, enhancing the system's resistance to heating. The TQC phase remains stable against next-nearest-neighbor (NNN) exchange perturbations and rotational imperfections, with robustness comparable to discrete time crystals (TCs) under periodic driving. Our results establish this quasiperiodically driven system as a platform for long-lived nonequilibrium temporal order, revealing the interplay of disorder, collective rigidity, and quasiperiodic driving.