High-Efficiency Evaporative Cooling of Ultracold NaRb Molecules Assisted by Double Microwave Dressing

While the production of ground-state ultracold polar molecules via magneto-association of ultracold atoms has become a mature technique, the near-universal two-body collisional loss presents a significant challenge for further evaporative cooling toward quantum degeneracy. In this work, using the recently developed double microwave dressing technique, we achieve more than 1000-fold suppression of loss while maintaining a high good-to-bad collision ratio. This has allowed us to carry out efficient evaporative cooling in an optical trap with an efficiency higher than 2.5, ultimately leading to the observation of Bose-Einstein condensation (BEC) of NaRb molecules. Together with the earlier NaCs BEC experiment, our results demonstrate that the double microwave dressing technique provides a general pathway toward achieving quantum degeneracy in bosonic ultracold polar molecules.