Controlling the Scattering Length of Ultracold Dipolar Molecules

By applying a circularly polarized and slightly blue-detuned microwave field with respect to the first excited rotational state of a dipolar molecule, one can engineer a long-range, shallow potential well in the entrance channel of the two colliding partners. As the applied microwave ac field is increased, the longrange well becomes deeper and can support a certain number of bound states, which in turn bring the value of the molecule-molecule scattering length from a large negative value to a large positive one. We adopt an adimensional approach where the molecules are described by a resealed rotational constant (B) over tilde = B/s(E3) where s(E3) is a characteristic dipolar energy. We found that molecules with (B) over tilde > 10(8) are immune to any quenching losses when a sufficient ac field is applied, the ratio elastic to quenching processes can reach values above 10(3), and that the value and sign of the scattering length can be tuned. The ability to control the molecular scattering length opens the door for a rich, strongly correlated, many-body physics for ultracold molecules, similar to that for ultracold atoms.