Field-linked resonances of polar molecules*

We observed a novel type of scattering resonances related to "field-linked" bound states between two polar molecules. We use a microwave field addressing the J = 0 to J = 1 rotational transitions of the ground state NaK molecules to induce a long-range potential between the molecules. The interaction potential can be described by a van der Waals interaction plus a dipole-dipole interaction. The former shields the molecules against destructive short-range collisions, and together with the latter, hosts the "field-linked" bound states. We measured the resonance feature related to these bound states in both inelastic and elastic scattering, and observed orders of magnitude tunability over the collision rates. The field-linked resonance demonstrated here is universal and could be applied to a wide range of polar molecules, providing a general method to control the intermolecular interactions as well as to assemble ultracold polyatomic molecules.