High Resolution Molecular Spectroscopy for Producing Ultracold Absolute Ground-State $^{23}$Na$^{87}$Rb Molecules

TL;DR

This study provides detailed high-resolution spectroscopy of NaRb molecules, enabling precise identification of states for efficient transfer to the absolute ground state, advancing ultracold molecule production.

Contribution

It reports the first detailed spectroscopic analysis of excited states of NaRb for ground-state molecule formation, including the identification of a hyperfine-coupled level and precise measurement of its binding energy.

Findings

Identified a hyperfine-coupled level suitable for population transfer.

Measured the binding energy of the level with high precision.

Demonstrated successful Raman transfer to the molecular ground state.

Abstract

We report a detailed molecular spectroscopy study on the lowest excited electronic states of $^{23}\rm{Na}^{87}\rm{Rb}$ for producing ultracold $^{23}\rm{Na}^{87}\rm{Rb}$ molecules in the electronic, rovibrational and hyperfine ground state. Starting from weakly-bound Feshbach molecules, a series of vibrational levels of the $A^{1}\Sigma^{+}-b^{3}\Pi$ coupled excited states were investigated. After resolving, modeling and interpreting the hyperfine structure of several lines, we successfully identified a long-lived level resulting from the accidental hyperfine coupling between the $0^+$ and $0^-$ components of the $b^3\Pi$ state, satisfying all the requirements for the population transfer toward the lowest rovibrational level of the X$^1\Sigma^+$ state. Using two-photon spectroscopy, its binding energy was measured to be 4977.308(3) cm$^{-1}$, the most precise value to date. We calibrated all the transition strengths carefully and also demonstrated Raman transfer of Feshbach molecules to the absolute ground state.