# Singlet Pathway to the Ground State of Ultracold Polar Molecules

## TL;DR

The paper presents a new two-photon pathway to produce ultracold polar molecules in their ground state using only singlet-to-singlet optical transitions, simplifying the process by avoiding complex intermediate state searches.

## Contribution

It introduces a novel singlet pathway that bypasses the need for hyperfine mixing, enabling efficient transfer to the ground state in bi-alkali molecules.

## Key findings

- Successfully demonstrated the pathway with ${}^{6} extrm{Li}{}^{40} extrm{K}$ molecules.
- Achieved large, balanced Rabi frequencies for both transitions.
- Method applicable to other molecular species.

## Abstract

Starting from weakly bound Feshbach molecules, we demonstrate a two-photon pathway to the dipolar ground state of bi-alkali molecules that involves only singlet-to-singlet optical transitions. This pathway eliminates the search for a suitable intermediate state with sufficient singlet-triplet mixing and the exploration of its hyperfine structure, as is typical for pathways starting from triplet dominated Feshbach molecules. By selecting a Feshbach state with a stretched singlet hyperfine component and controlling the polarization of the excitation laser, we assure coupling to only a single hyperfine component of the $\textrm{A}^{1}\Sigma^{+}$ excited potential, even if the hyperfine structure is not resolved. Similarly, we address a stretched hyperfine component of the $\textrm{X}^{1}\Sigma^{+}$ rovibrational ground state, and therefore an ideal three level system is established. We demonstrate this pathway with ${}^{6}\textrm{Li}{}^{40}\textrm{K}$ molecules. By exploring deeply bound states of the $\textrm{A}^{1}\Sigma^{+}$ potential, we are able to obtain large and balanced Rabi frequencies for both transitions. This method can be applied to other molecular species.