Two-Photon Pathway to NaCs Ground State Molecules

We report on the creation of an ultracold ensemble of ground state sodium-cesium (NaCs) molecules. To identify intermediate states suitable for stimulated Raman adiabatic passage (STIRAP), we study bound-to-bound transitions starting from Feshbach molecules [1]. Continuously covering a spectrum of 14 THz, we group lines based on internal structure and observe lines with exceptionally large linewidths greater than 1 GHz. We assign quantum numbers to these intermediate states. We perform detailed one- and two-photon studies on the B¹Π and c³Σ⁺ lines and identify a bridge to the X¹Σ⁺ ground state. Using this pathway, we observe 70% transfer efficiency to the rovibrational ground state.