The hyperfine energy levels of alkali metal dimers: ground-state homonuclear molecules in magnetic fields

TL;DR

This paper studies hyperfine energy levels and Zeeman splittings of homonuclear alkali-metal dimers, providing detailed theoretical calculations relevant for quantum gas experiments involving these molecules.

Contribution

It offers the first comprehensive DFT-based analysis of hyperfine interactions in homonuclear alkali dimers across various rotational states.

Findings

Zero-field splittings mainly due to scalar nuclear spin-spin coupling.

Nuclear spin remains a good quantum number in magnetic fields for homonuclear molecules.

Rotational N=1 states show complex Zeeman splittings dominated by nuclear quadrupole interactions.

Abstract

We investigate the hyperfine energy levels and Zeeman splittings for homonuclear alkali-metal dimers in low-lying rotational and vibrational states, which are important for experiments designed to produce quantum gases of deeply bound molecules. We carry out density-functional theory (DFT) calculations of the nuclear hyperfine coupling constants. For nonrotating states, the zero-field splittings are determined almost entirely by the scalar nuclear spin-spin coupling constant. By contrast with the heteronuclear case, the total nuclear spin remains a good quantum number in a magnetic field. We also investigate levels with rotational quantum number N = 1, which have long-range anisotropic quadrupole-quadrupole interactions and may be collisionally stable. For these states the splitting is dominated by nuclear quadrupole coupling for most of the alkali-metal dimers and the Zeeman splittings are considerably more complicated.