Coherent optical creation of a single molecule in an optical tweezer*

Diverse species of ultracold molecules are desired for a variety of applications in precision measurement, quantum simulation, quantum information processing and ultracold chemistry. Coherent association of ultracold atoms into a molecule typically requires special properties, such as the availability of a magnetic Feshbach resonance, narrow-line excited states or weakly-bound states at the MHz level, which limits the applicability of the technique. Here, we present a more general technique, where we associate the atoms using a coherent two-photon Raman transition. In particular, we form a NaCs molecule in an optical tweezer from ground state cooled Na and Cs atoms. We systematically study the excited state landscape and the possible initial and final states for the most favorable set of parameters to perform the transfer. With these parameters and technical insights, including the use of a narrow-band optical filter, we demonstrate Rabi oscillations between the free atoms and weakly bound molecules. We achieve a transfer efficiency of 69%. Our technique should allow a wider range of molecular species to be assembled atom-by-atom.