Isotope-selective trapping of doubly charged Yb ions

We report isotope-selective loading and trapping of doubly ionized ytterbium into an rf quadrupole trap. Isotopically pure clouds of 174Yb+ ions were first loaded into the rf trap via a multistage photoionization process. The Yb2+ ions were then produced by electron impact ionization of the trapped Yb+ ions. The Yb2+ ions were subsequently detected by rf excitation of their secular motion in the trap, which led to sympathetic heating and changes in the fluorescence of the laser-cooled Yb+ ions. The presence of doubly charged Yb ions was further verified by the appearance of a dark band in the center of Yb+ ion cloud after electron impact ionization. We discuss the possible formation of Yb2+H and similar compounds and the schemes for the direct optical detection of the Yb2+ ions.