Eigenstate thermalization scaling in approaching the classical limit

• URL: http://arxiv.org/abs/2012.06361v1
• Date: Fri, 11 Dec 2020 14:02:22 GMT
• Title: Eigenstate thermalization scaling in approaching the classical limit
• Authors: Goran Nakerst and Masudul Haque
• Abstract summary: We study a different limit - the classical or semiclassical limit - by increasing the particle number in fixed lattice topologies. We show numerically that, for larger lattices, ETH scaling of physical mid-spectrum eigenstates follows the ideal (Gaussian) expectation, but for smaller lattices, the scaling occurs via a different exponent.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: According to the eigenstate thermalization hypothesis (ETH), the eigenstate-to-eigenstate fluctuations of expectation values of local observables should decrease with increasing system size. In approaching the thermodynamic limit - the number of sites and the particle number increasing at the same rate - the fluctuations should scale as $\sim D^{-1/2}$ with the Hilbert space dimension $D$. Here, we study a different limit - the classical or semiclassical limit - by increasing the particle number in fixed lattice topologies. We focus on the paradigmatic Bose-Hubbard system, which is quantum-chaotic for large lattices and shows mixed behavior for small lattices. We derive expressions for the expected scaling, assuming ideal eigenstates having Gaussian-distributed random components. We show numerically that, for larger lattices, ETH scaling of physical mid-spectrum eigenstates follows the ideal (Gaussian) expectation, but for smaller lattices, the scaling occurs via a different exponent. We examine several plausible mechanisms for this anomalous scaling.

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