Towards the Dipolar Ground State of ⁶Li⁴⁰K

We demonstrate a two-photon pathway to the ground state of ⁶Li⁴⁰K molecules that involves only singlet-to-singlet optical transitions. We start from a molecular state which contains a significant admixture from the singlet ground state potential by selecting the Feshbach resonance for molecule association. With the only contributing singlet state to the molecular state being fully stretched and with control over the lasers polarization we address a sole hyperfine component of the excited A¹Σ⁺ potential without resolving its hyperfine structure. We perform dark resonance spectroscopy to precisely determine the transition frequencies of the states involved. The strong dipolar nature of ⁶Li⁴⁰K is revealed by Stark spectroscopy, as it is necessary for the study of dipolar interactions in an optical lattice. The two Raman lasers utilized for the Stimulated Raman Adiabatic Passage (STIRAP) are locked to a high finesse cavity using the Pound-Drever-Hall lock. The finesse of the cavity is measured at 665nm and 1119nm via the cavity ring-down method. The linewidths of the two Raman lasers are determined by recording their beat frequencies to an ultralow-noise frequency comb in the neighboring group. We perform the phase noise measurement of the Raman lasers. We estimate the contributions from different STIRAP loss mechanisms and propose several improvements to the current Raman laser system towards a successful transfer to the dipolar ground state.