Spin-exchange and spin-relaxation in ultracold Rb-Sr$^+$ collisions

We present a joint experimental and theoretical study of collision-induced spin exchange and spin relaxation of a single trapped Sr$^+$ ion immersed in an ultracold gas of Rb atoms in different hyperfine states. We find that inelastic spin-relaxation of Sr$^+$ caused by the second-order spin-orbit coupling occurs much more slowly than in Rb-Yb$^+$ collisions. The calculated spin exchange rates are very sensitive to small variations of the Rb-Sr$^+$ interaction potential even in the multiple-partial-wave regime due to an unexpected correlation between the singlet and triplet scattering phase shifts.