Spatial separation of ion clouds between sympathetically laser-cooled Cd⁺ -ion isotopes in a Penning trap

Natural Cd⁺ ions in a Penning trap are cooled sympathetically below 1 K by a Coulomb interaction with directly laser-cooled Be⁺ ions. Spatial separation of the Be⁺ and Cd⁺ ion clouds due to centrifugal force is observed directly. When the frequency of rotation of the ion clouds is accelerated, the separation between Cd⁺ -ion isotopes (A=110 and 116) can be clearly observed, though their mass difference is very small. The equations of motion for 100 Be⁺ ions and 50 Cd⁺ ions are solved to simulate the experiments, and the result shows the spatial separation between the two ion species. The separation between the Cd⁺ -ion isotopes is investigated by comparing the experimental results with numerical calculations.