Observation of magnetically tunable resonances in ultracold ⁴⁰K⁸⁷Rb + ⁸⁷Rb mixtures

Scattering resonances between ultracold atoms and molecules offer new opportunities to study ultracold collisions and chemistry. In this work, we search for magnetically tunable Feshbach resonances in ultracold mixtures of ⁴⁰K⁸⁷Rb + ⁸⁷Rb across a broad range of magnetic fields with KRb molecules prepared in four different hyperfine levels of the rovibrational ground state. We observe various magnetic field-dependent enhanced loss features, some of which are sharp while others are broad and may reflect a near continuum of resonances. By combining measurements of the loss rate with direct detection of the intermediate complexes formed in these collisions, our experimental results open new questions in the loss mechanism of ultracold collisions involving molecules and atoms.