Observation of Fano-suppression in scattering resonances of dipolar spin mixtures

Lanthanide atoms, such as erbium and dysprosium, feature unique properties compared to alkali atoms, including strong dipole-dipole interactions, a large spin manifold in their absolute ground state, and complex collisional behavior in the ultracold regime. Using a sequence of Rabi pulses of a clock-like transition at 1299nm, we gain full control over the initial spin composition of the system. This allows us to study dipolar scattering involving different spin channels.

In particular, we observe multiple inter- and intra-spin Fano-Feshbach scattering resonances. Most notably, some resonances feature a distinct asymmetric Fano shape with a pronounced loss minimum. This shape indicates quantum interference between different scattering paths during the collision which leads to a suppression of losses.  Our observations are confirmed by a square-well model which - despite its simplicity - captures the key mechanism of the Fano interference. The observed suppression of losses of more than one order of magnitude while keeping the elastic scatting length finite paves the way to explore phenomena arising from spin-spin interactions in stable dipolar systems.