Evaporation of microwave-shielded polar molecules to quantum degeneracy

TL;DR

This paper demonstrates the first evaporative cooling of a three-dimensional gas of fermionic polar molecules to quantum degeneracy using microwave shielding, enabling exploration of exotic many-body quantum phenomena.

Contribution

It introduces a microwave shielding technique that stabilizes molecules and achieves deep cooling into the quantum degenerate regime, a significant advancement over previous methods.

Findings

Achieved molecular cooling to 21 nanokelvin, below the Fermi temperature.

Established a high elastic-to-inelastic collision ratio (>460).

Demonstrated stabilization of molecules against short-range collisions with microwave dressing.

Abstract

Ultracold polar molecules offer strong electric dipole moments and rich internal structure, which makes them ideal building blocks to explore exotic quantum matter, implement novel quantum information schemes, or test fundamental symmetries of nature. Realizing their full potential requires cooling interacting molecular gases deeply into the quantum degenerate regime. However, the complexity of molecules which makes their collisions intrinsically unstable at the short range, even for nonreactive molecules, has so far prevented the cooling to quantum degeneracy in three dimensions. Here, we demonstrate evaporative cooling of a three-dimensional gas of fermionic sodium-potassium 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 nanokelvin, corresponding to 0.36 times the Fermi temperature. Such unprecedentedly cold and dense samples of polar molecules open the path to the exploration of novel many-body phenomena, such as the long-sought topological p-wave superfluid states of ultracold matter.