Spectroscopy of $^{87}\text{Sr}$ triplet Rydberg states

TL;DR

This study combines experimental measurements and theoretical analysis to characterize high-$n$ triplet Rydberg states in $^{87}$Sr, addressing hyperfine interactions that challenge precision spectroscopy and theoretical modeling.

Contribution

It provides a non-perturbative evaluation of hyperfine shifts for high-$n$ $^{87}$Sr$^*$ states using $^{88}$Sr data, and refines quantum defect values for $^{3} ext{D}$ states.

Findings

Good agreement between measurements and theory for hyperfine shifts.

Extraction of $^{3} ext{D}$ state energies for isotopes without hyperfine structure.

Refined quantum defect values for high-$n$ Rydberg states.

Abstract

A combined experimental and theoretical spectroscopic study of high-$n$, ${30 \lesssim n \lesssim 100}$, triplet $\text{S}$ and $\text{D}$ Rydberg states in $^{87}\text{Sr}$ is presented. $^{87}\text{Sr}$ has a large nuclear spin, ${I=9/2}$, and at high-$n$ the hyperfine interaction becomes comparable to, or even larger than, the fine structure and singlet-triplet splittings which poses a considerable challenge both for precision spectroscopy and for theory. For high-$n$ $\text{S}$ states, the hyperfine shifts are evaluated non-perturbatively taking advantage of earlier spectroscopic data for the ${I=0}$ isotope $^{88}\text{Sr}$, which results in good agreement with the present measurements. For the $\text{D}$ states, this procedure is reversed by first extracting from the present $^{87}\text{Sr}$ measurements the energies of the $^{3}\text{D}_{1,2,3}$ states to be expected for isotopes without hyperfine structure ($^{88}\text{Sr}$) which allows the determination of corrected quantum defects in the high-$n$ limit.