Resonant Dipolar Collisions of Ultracold Molecules Induced by Microwave Dressing

We demonstrate microwave dressing on ultracold, fermionic {}^{23}a{}^{40} ground-state molecules and observe resonant dipolar collisions with cross sections exceeding three times the swave unitarity limit. The origin of these collisions is the resonant alignment of the approaching molecules' dipoles along the intermolecular axis, which leads to strong attraction. We explain our observations with a conceptually simple two-state picture...