Observation of Bose-Einstein Condensate of dipolar NaRb molecules*

Exotic quantum phases have been theoretically predicted in quantum gases of polar molecules due to their long-range dipole-dipole interactions. However, realizing these phases requires achieving quantum degeneracy of molecular quantum gas. The development of double microwave shielding has made it possible to bring molecular quantum gas into the quantum degenerate regime while allowing precise control over inter-molecular interactions [1-4]. By suppressing two- and three-body losses through double microwave shielding, we perform efficient forced evaporative cooling of NaRb molecules, achieving an evaporation efficiency exceeding 2.5. As the molecular gas cools, a bimodal distribution emerges, signaling Bose-Einstein condensation (BEC). Further evaporation increases the BEC fraction to 70%. Additionally, by tuning the dipole-dipole interaction, we observe the formation of self-bound droplets, a novel phase of dipolar molecules. Our work paves the way for exploring strongly correlated quantum phases in ultracold molecular gases.

Reference:

[1] Bigagli, Niccolo, et al. "Observation of Bose–Einstein condensation of dipolar molecules." Nature (2024): 1-5.

[2]  Schindewolf, Andreas, et al. "Evaporation of microwave-shielded polar molecules to quantum degeneracy." Nature 607.7920 (2022): 677-681.

[3]  Lin, Junyu, et al. "Microwave shielding of bosonic NaRb molecules." Physical Review X 13.3 (2023): 031032.

[4   Bigagli, Niccolo, et al. "Collisionally stable gas of bosonic dipolar ground-state molecules." Nature Physics 19.11 (2023): 1579-1584.