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Journal Article

Eigenstate thermalization scaling in approaching the classical limit


Haque,  Masudul
Max Planck Institute for the Physics of Complex Systems, Max Planck Society;

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Nakerst, G., & Haque, M. (2021). Eigenstate thermalization scaling in approaching the classical limit. Physical Review E, 103(4): 042109. doi:10.1103/PhysRevE.103.042109.

Cite as: https://hdl.handle.net/21.11116/0000-0008-EC23-7
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 similar to 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 midspectrum 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.