Ultracold Long-Range Rydberg Molecules with Complex Multichannel Spectra

A generalized class of exotic long-range Rydberg molecules consisting of a multichannel Rydberg atom bound to a distant ground state atom by the Rydberg electron is predicted. These molecules are characterized by the rich physics provided by the strongly perturbed multichannel Rydberg spectra of divalent atoms, in contrast to the regular Rydberg series of the alkali atoms used to form Rydberg molecules to date. These multichannel Rydberg molecules exhibit favorable properties for laser excitation, because states exist where the quantum defect varies strongly with the principal quantum number $n$. In particular, the $nd$ Rydberg state of calcium becomes nearly degenerate with states of high orbital angular momentum over the range $17