Singlet Pathway to the Ground State of Ultracold Polar Molecules

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 ${\text{A}}^1\hat{I}{\pounds }^{+}$ excited potential, even if the hyperfine structure is not resolved. Similarly, we address a stretched hyperfine component of the ${\text{X}}^1\hat{I}{\pounds }^{+}$ rovibrational ground state, and therefore an ideal three level system is established. We demonstrate this pathway with ${}^6\text{Li}{}^{40}\text{K}$ molecules. By exploring deeply bound states of the ${\text{A}}^1\hat{I}{\pounds }^{+}$ potential, we are able to obtain large and balanced Rabi frequencies for both transitions. This method can be applied to other molecular species.

manuscript and supplemental material