Eigenstate thermalization to non-Gibbs states in strongly-interacting chaotic lattice gases*

We demonstrate [1] that equilibrium energy distributions in many-body chaotic systems can be qualitatively different from the Fermi-Dirac and Bose-Einstein distributions. This effect can appear in systems with finite energy spectra, which support both positive and negative temperatures, in the regime of quantum degeneracy, when the eigenstates fill a substantial part of the Hilbert space. The results are supported by  exact diagonalization calculations for chaotic Fermi-Hubbard and Bose-Hubbard models, when they have Wigner-Dyson statistics of energy spectra and demonstrate eigenstate thermalization. The proposed effects may be observed in experiments with cold atoms in optical lattices.

1. Vladimir A. Yurovsky and Amichay Vardi, arXiv:2501.08967