Diffusive scaling of Rényi entanglement entropy

Abstract

Recent studies found that the diffusive transport of conserved quantities in non-integrable many-body systems has an imprint on quantum entanglement: while the von Neumann entropy of a state grows linearly in time $t$ under a global quench, all $n$th Rényi entropies with $n>1$ grow with a diffusive scaling $\sqrt{t}$. To understand this phenomenon, we introduce an amplitude $A(t)$, which is the overlap of the time-evolution operator $U(t)$ of the entire system with the tensor product of the two evolution operators of the subsystems of a spatial bipartition. As long as $|A(t)|\ge e^{-\sqrt{Dt}}$, which we argue holds true for generic diffusive non-integrable systems, all $n$th Rényi entropies with $n>1$ (annealed-averaged over initial product states) are bounded from above by $\sqrt{t}$. We prove the following inequality for the disorder average of the amplitude, $\overline{|A(t)|}\ge e^{-\sqrt{Dt}}$, in a local spin-$\frac{1}{2}$ random circuit with a $\text{U}(1)$ conservation law by mapping to the survival probability of a symmetric exclusion process. Furthermore, we numerically show that the typical decay behaves asymptotically, for long times, as $|A(t)|\sim e^{-\sqrt{Dt}}$ in the same random circuit as well as in a prototypical non-integrable model with diffusive energy transport but no disorder.

9 pages, 4 figures, published version with minor changes

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• Transport and entanglement growth in long-range random Clifford circuits
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• Dynamics of Rényi entanglement entropy in diffusive qudit systems
• Coarse-grained Entanglement and Operator Growth in Anomalous Dynamics
• Semiclassical Limit of Measurement-Induced Transition in Many-Body Chaos in Integrable and Nonintegrable Oscillator Chains
• Entanglement Dynamics From Random Product States: Deviation From Maximal Entanglement
• Entanglement dynamics of multi-parametric random states: a single parametric formulation