Cooling a trapped ion to a temperature that enables coherent operations requires a closed laser excitation scheme, which usually limits applications to ions with a single valence electron in an s-orbital. This vastly limits the available level structures for the implementation of qubits. Singly-charged ¹⁶⁹Tm⁺ (Z=69) has a nuclear spin of 1/2 and is an effective two-electron system with a long-lived metastable state at only 237 cm^-1 above the ground state, which is directly accessible through a common excited state. This makes it an interesting candidate for the implementation of higher order qudits and serves as a proof-of-principle for the applicability of complex electronic structures for quantum computing.

We report on our recent progress to trap and laser cool single ¹⁶⁹Tm⁺ ions and discuss different cooling schemes as well as potential implementations of state preparation and measurement (SPAM) schemes, qudits and qudit gates in the unique level structure. This contribution also includes a short technical overview of the ion trap and laser setup.