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arXiv · 2009.10104

Scrambling and Lyapunov Exponent in Unitary Networks with Tunable Interactions

Anna Keselman·Laimei Nie·Erez Berg
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Abstract

Scrambling of information in a quantum many-body system, quantified by the out-of-time-ordered correlator (OTOC), is a key manifestation of quantum chaos. A regime of exponential growth in the OTOC, characterized by a Lyapunov exponent, has so far mostly been observed in systems with a high-dimensional local Hilbert space and in weakly-coupled systems. Here, we propose a general criterion for the existence of a well-defined regime of exponential growth of the OTOC in spatially extended systems with local interactions. In such systems, we show that a parametrically long period of exponential growth requires the butterfly velocity to be much larger than the Lyapunov exponent times a microscopic length scale, such as the lattice spacing. As an explicit example, we study a random unitary circuit with tunable interactions. In this model, we show that in the weakly interacting limit the above criterion is satisfied, and there is a prolonged window of exponential growth. Our results are based on numerical simulations of both Clifford and universal random circuits supported by an analytical treatment.

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Anna Keselman, Laimei Nie, Erez Berg. 2020-09-21. Scrambling and Lyapunov Exponent in Unitary Networks with Tunable Interactions. https://doi.org/10.1103/physrevb.103.l121111

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