A pathway to ultracold bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ ground state molecules

TL;DR

This paper demonstrates a spectroscopic method to convert ultracold NaK molecules into their rovibronic ground state using STIRAP, identifying key intermediate states and their properties for efficient molecule formation.

Contribution

It provides a detailed spectroscopic characterization of intermediate states and a complete scheme for creating ultracold NaK molecules in their ground state.

Findings

Identification of mixed excited states suitable for STIRAP

Determination of the ground state and hyperfine structure

Measurement of transition dipole moments

Abstract

We spectroscopically investigate a pathway for the conversion of $^{23}\textrm{Na}^{39}\textrm{K}$ Feshbach molecules into rovibronic ground state molecules via STImulated Raman Adiabatic Passage (STIRAP). Using photoassociation spectroscopy from the diatomic scattering threshold in the $a^3\Sigma^+$ potential, we locate the resonantly mixed electronically excited intermediate states $|B^1\Pi, v=8\rangle$ and $|c^3\Sigma^+, v=30\rangle$ which, due to their singlet-triplet admixture, serve as an ideal bridge between predominantly $a^3\Sigma^+$ Feshbach molecules and pure $X^1\Sigma^+$ ground state molecules. We investigate their hyperfine structure and present a simple model to determine the singlet-triplet coupling of these states. Using Autler-Townes spectroscopy, we locate the rovibronic ground state of the $^{23}\textrm{Na}^{39}\textrm{K}$ molecule ($|X^1\Sigma^+, v=0, N=0\rangle$) and the second rotationally excited state $N=2$ to unambiguously identify the ground state. We also extract the effective transition dipole moment from the excited to the ground state. Our investigations result in a fully characterized scheme for the creation of ultracold bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ ground state molecules.