QUROPE Quantum Information Processing and Communication in Europe

We focus down an ion beam consisting of single 40Ca+ ions to a spot size of a few micrometers using an einzel lens. Starting from a segmented linear Paul trap, we have implemented a procedure that allows us to deterministically load a predetermined number of ions by using the potential shaping capabilities of our segmented ion trap. For single-ion loading, an efficiency of 96.7(7)% has been achieved. These ions are then deterministically extracted out of the trap and focused down to a 1σ-spot radius of (4.6±1.3) μm at a distance of 257 mm from the trap center. Compared to previous measurements without ion optics, the einzel lens is focusing down the single-ion beam by a factor of 12. Due to the small beam divergence and narrow velocity distribution of our ion source, chromatic and spherical aberration at the einzel lens is vastly reduced, presenting a promising starting point for focusing single ions on their way to a substrate.