Deeply bound (24$D_J$ + 5$S_{1/2}$) $^{87}$Rb and $^{85}$Rb molecules for eight spin couplings

TL;DR

This study reports the observation and detailed spectroscopic analysis of long-range Rydberg molecules formed by $^{85}$Rb and $^{87}$Rb, revealing insights into spin-dependent interactions and scattering properties.

Contribution

It provides the first comprehensive measurement of eight spin-coupled Rydberg molecules and determines all relevant scattering length functions from experimental data.

Findings

Binding energies up to 440 MHz with sub-percent uncertainty

Isotopic effects influence molecular binding energies

All four scattering length functions are determined from data

Abstract

We observe long-range $^{85}$Rb and $^{87}$Rb (24$D$+5$S_{1/2}$) Rydberg molecules for eight different spin couplings, with binding energies up to 440~MHz and sub-percent relative uncertainty. Isotopic effects of the molecular binding energies arise from the different masses and nuclear spins. Because the vibrational states involve different spin configurations and cover a wide range of internuclear separations, the states have different dependencies on the $s$-wave and $p$-wave scattering phase shifts for singlet and triplet scattering. Fitting the spectroscopic data, we comprehensively determine all four scattering length functions over the relevant energy range as well as the zero-energy scattering lengths of the two $s$-wave channels. Our unusually high temperature and low density (180 $\mu$K, 1 $\times$ 10$^{11}$ cm$^{-3}$) suggest that the molecule excitation occurs through photoassisted collisions.