Field-linked resonances of polar molecules

Scattering resonances are an essential tool for controlling the interactions of ultracold atoms and molecules. However, conventional Feshbach scattering resonances(1), which have been extensively studied in various platforms(1-7), are not expected to exist in most ultracold polar molecules because of the fast loss that occurs when two molecules approach at a close distance(8-10). Here we demonstrate a new type of scattering resonance that is universal for a wide range of polar molecules. The so-called field-linked resonances(11-14) occur in the scattering of microwave-dressed molecules because of stable macroscopic tetramer states in the intermolecular potential. We identify two resonances between ultracold ground-state sodium-potassium molecules and use the microwave frequencies and polarizations to tune the inelastic collision rate by three orders of magnitude, from the unitary limit to well below the universal regime. The field-linked resonance provides a tuning knob to independently control the elastic contact interaction and the dipole-dipole interaction, which we observe as a modification in the thermalization rate. Our result provides a general strategy for resonant scattering between ultracold polar molecules, which paves the way for realizing dipolar superfluids(15) and molecular supersolids(16), as well as assembling ultracold polyatomic molecules.

Automated summary

Scattering resonances are a useful tool for controlling interactions of ultracold atoms and molecules. Conventional Feshbach scattering resonances are not expected to exist in most ultracold polar molecules due to fast loss during close approach. However, a new type of scattering resonance, called field-linked resonances, has been demonstrated to be universal for a wide range of polar molecules. These resonances provide a tuning knob for independently controlling elastic contact interaction and dipole-dipole interaction, leading to potential applications in dipolar superfluids and molecular supersolids.