Prediction of Feshbach resonances in collisions of ultracold rubidium atoms

On the basis of recently measured ${\mathrm{Rb}}_2$ bound-state energies and continuum properties, we predict magnetically induced Feshbach resonances in collisions of ultracold rubidium atoms. The resonances make it possible to control the sign and magnitude of the effective particle-particle interaction in a Rb Bose-Einstein condensate by tuning a bias magnetic field. For the case of ${}^{85}\mathrm{Rb}$ they occur at field values in the range where these atoms can be magnetostatically trapped. For ${}^{87}\mathrm{Rb}$ they are predicted to occur at negative field values.