Evaporation of microwave-shielded polar molecules to quantum degeneracy

Collisional loss at short range has so far prevented the cooling of interacting polar molecules to quantum degeneracy in three dimensions (3D). Here, we demonstrate evaporative cooling of a 3D gas of fermionic NaK molecules to well below the Fermi temperature using microwave shielding. The molecules are protected from reaching short range with a repulsive barrier engineered by coupling rotational states with a blue-detuned circularly polarized microwave. The microwave dressing induces strong tunable dipolar interactions between the molecules, leading to high elastic collision rates that can exceed the inelastic ones by at least a factor of 460. This large elastic-to-inelastic collision ratio allows us to cool the molecular gas down to 21 nK, corresponding to 0.36 times the Fermi temperature.

arXiv:2201.05143