Robust effective ground state in a nonintegrable Floquet quantum circuit

Abstract

An external periodic (Floquet) drive is believed to bring any initial state to the featureless infinite temperature state in generic nonintegrable isolated quantum many-body systems in the thermodynamic limit, irrespective of the driving frequency $\Omega$. However, numerical or analytical evidence either proving or disproving this hypothesis is very limited and the issue has remained unsettled. Here, we study the initial state dependence of Floquet heating in a nonintegrable kicked Ising chain of length up to $L=30$ with an efficient quantum circuit simulator, showing a possible counterexample: The ground state of the effective Floquet Hamiltonian is exceptionally robust against heating, and could stay at finite energy density even after infinitely many Floquet cycles, if the driving period is shorter than a threshold value. This sharp energy localization transition/crossover does not happen for generic excited states. The exceptional robustness of the ground state is interpreted by (i) its isolation in the energy spectrum and (ii) the fact that those states with $L$-independent $\hslash \Omega$ energy above the ground state energy of any generic local Hamiltonian, like the approximate Floquet Hamiltonian, are atypical and viewed as a collection of noninteracting quasipartiles. Our finding paves the way for engineering Floquet protocols with finite driving periods realizing long-lived, or possibly even perpetual, Floquet phases by initial state design.

5+12 pages, 4+10 figures

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Cited by in corpus (9)

• Geometric Floquet theory
• Theory of metastable states in many-body quantum systems
• Sharp detection of the onset of Floquet heating using eigenstate sensitivity
• Floquet theory and applications in open quantum and classical systems
• Nonperturbative decay of bipartite discrete time crystals
• Prethermalization, shadowing breakdown, and the absence of Trotterization transition in quantum circuits
• Unpolarized prethermal discrete time crystal
• Finding periodic orbits in projected quantum many-body dynamics
• Trotter transition in BCS pairing dynamics