Avoided crossings between bound states of ultracold Cesium dimers

TL;DR

This paper introduces a new computational method for efficiently calculating the bound states of ultracold Cs_2 molecules in magnetic fields, improving over previous basis set approaches and enabling detailed analysis of avoided crossings.

Contribution

The authors develop a basis-set-free propagation method that enhances efficiency and accuracy in modeling ultracold alkali-metal dimers, especially near avoided crossings.

Findings

Successfully characterized avoided crossings in Cs_2

Observed discrepancies with experimental data in crossing strengths and level positions

Method allows inclusion of many spin channels for better modeling

Abstract

We present an efficient new computational method for calculating the binding energies of the bound states of ultracold alkali-metal dimers in the presence of magnetic fields. The method is based on propagation of coupled differential equations and does not use a basis set for the interatomic distance coordinate. It is much more efficient than the previous method based on a radial basis set and allows many more spin channels to be included. This is particularly important in the vicinity of avoided crossings between bound states. We characterize a number of different avoided crossings in Cs_2 and compare our converged calculations with experimental results. Small but significant discrepancies are observed in both crossing strengths and level positions, especially for levels with l symmetry (rotational angular momentum L=8). The discrepancies should allow the development of improved potential models in the future.