Effective many-body parameters for atoms in non-separable Gaussian optical potentials

TL;DR

This paper develops numerical methods to analyze particles in complex 3D Gaussian optical potentials, accounting for anharmonicity and non-separability, with applications to ultracold atom experiments.

Contribution

It introduces optimized DVR-based numerical techniques and a framework for quantifying non-separability, advancing modeling of ultracold atoms in realistic optical potentials.

Findings

Efficient DVR methods with symmetry and variational enhancements.

Quantitative measures of eigenstate non-separability.

Construction of localized Wannier functions and matrix elements.

Abstract

We analyze the properties of particles trapped in three-dimensional potentials formed from superimposed Gaussian beams, fully taking into account effects of potential anharmonicity and non-separability. Although these effects are negligible in more conventional optical lattice experiments, they are essential for emerging ultracold atom developments. We focus in particular on two potentials utilized in current ultracold atom experiments: arrays of tightly focused optical tweezers and a one-dimensional optical lattice with transverse Gaussian confinement and highly excited transverse modes. Our main numerical tools are discrete variable representations (DVRs), which combine many favorable features of spectral and grid-based methods, such as the computational advantage of exponential convergence and the convenience of an analytical representation of Hamiltonian matrix elements. Optimizations, such as symmetry adaptations and variational methods built on top of DVR methods, are presented and their convergence properties discussed. We also present a quantitative analysis of the degree of non-separability of eigenstates, borrowing ideas from the theory of matrix product states (MPSs), leading to both conceptual and computational gains. Beyond developing numerical methodologies, we present results for construction of optimally localized Wannier functions and tunneling and interaction matrix elements in optical lattices and tweezers relevant for constructing effective models for many-body physics.