Precision Spectroscopy in Yb+ ions

We report on our progress on multi-ion spectroscopy with Yb⁺ions. We first characterized the spatial homogeneity of the magnetic- and the rf-field. Subsequently, to equalize the immense AC Stark shifts of the individual ions in a Coulomb crystal, we utilize a holographic phase plate to convert the Gaussian beam into a flat-top shape. These efforts enable us to excite an 8-ion crystal (¹⁷²Yb⁺) on the highly forbidden electric octupole transition. Using 173Yb+ with reduced AC Stark shift, the same beam profile could support the multi-ion operation of 20 ions. This paves the way for future multi-ion optical clocks.