Analysis of light-induced frequency shifts in the photoassociation of ultracold metastable helium atoms

TL;DR

This paper provides a detailed analysis of light-induced frequency shifts in photoassociation lines of ultracold metastable helium atoms, offering semi-analytical formulas that relate shifts to the scattering length, facilitating its measurement.

Contribution

It introduces a semi-analytical approach to quantify frequency shifts in ultracold helium, linking them explicitly to the scattering length, based on the system's simplicity and long-range potential properties.

Findings

Derived explicit linear dependence of shifts on scattering length a.

Validated the semi-analytical expressions with experimental data.

Simplified the analysis by exploiting the system's long-range potential and polarization.

Abstract

We present an exhaustive analysis of the light-induced frequency shifts of the photoassociation lines of ultracold metastable 4He* atoms in a magnetic trap. The measurements of the shifts of several vibrational levels bound in the purely long-range J=1,0u+ potential linked to the 23S1-23P0 asymptote were reported in a previous paper and are analyzed here. The simplicity of this system makes it very appropriate for a detailed study. Indeed, the purely long-range character of the excited potential allows one to calculate exact excited molecular wavefunctions and to use asymptotic expansions at large internuclear distances of the ground state wavefunctions appearing in Franck-Condon type integrals. Moreover, the number of collisional channels to be considered is strongly reduced by the absence of hyperfine structure for 4He* and the use of polarized ultracold atoms and polarized light. This allows us to derive semi-analytical expressions for the shifts showing explicitly their linear dependences on the s-wave scattering length a of spin polarized metastable 4He* atoms. This explains how it is possible to derive the measurement of a from these shifts.