Microscopic theory of the Hubbard interaction in low-dimensional optical lattices

TL;DR

This paper provides an exact calculation of the Hubbard on-site interaction in low-dimensional optical lattices, accounting for confinement and higher bands, revealing lattice-induced resonances and matching experimental data.

Contribution

It introduces a non-perturbative method to determine the Hubbard interaction considering transverse confinement and higher bands, surpassing standard approximations.

Findings

Hubbard interaction exhibits lattice-induced resonances at specific scattering lengths.

Results agree with spectroscopic measurements in quasi-two-dimensional optical lattices.

Method can be extended to multi-band models and other lattice-based atom interactions.

Abstract

The Hubbard model is a paradigmatic model of strongly correlated quantum matter, thus making it desirable to investigate with quantum simulators such as ultracold atomic gases. Here, we consider the problem of two atoms interacting in a quasi-one- or quasi-two-dimensional optical lattice, geometries which are routinely realized in quantum-gas-microscope experiments. We perform an exact calculation of the low-energy scattering amplitude which accounts for the effects of the transverse confinement as well as all higher Bloch bands. This goes beyond standard perturbative treatments and allows us to precisely determine the effective Hubbard on-site interaction for arbitrary $s$-wave scattering length (see source code available at [1]). In particular, we find that the Hubbard on-site interaction displays lattice-induced resonances for scattering lengths on the order of the lattice spacing, which are well within reach of current experiments. Furthermore, we show that our results are in excellent agreement with spectroscopic measurements of the Hubbard interaction for a quasi-two-dimensional square optical lattice in a quantum gas microscope. Our formalism is very general and may be extended to multi-band models and other atom-like scenarios in lattice geometries, such as exciton-exciton and exciton-electron scattering in moir\'e superlattices.