Zeeman metastable qubit operations in trapped ⁴⁰Ca⁺ ions

Dual-species trapped ion experiments provide benefits such as sympathetic cooling and ancilla readout without unwanted crosstalk and decoherence from scattered resonant photons. However, the different masses and transition frequencies of unlike ions introduce new technical challenges such as trap anharmonicities and the need for additional lasers. By encoding qubits in sublevels (hyperfine or Zeeman) of both the ground state and a long-lived metastable state, we achieve the benefits of multi-species operation within ions of a single species. Here, we investigate a metastable qubit stored in Zeeman sublevels of the 3D_5/2 state of ⁴⁰Ca⁺ ions. Operations on a neighboring ground-state ⁴⁰Ca⁺ qubit can then be performed with minimal crosstalk. Metastable qubit gates are performed with RF pulses that drive transitions between two sublevels of the metastable state. The energy splittings between the six Zeeman levels are equal, so a laser is used to shift other levels out of resonance with the RF pulses. We also describe progress towards sympathetic cooling with a co-trapped ground state ion, as well as the potential for using the full Hilbert space of both the ground and metastable levels for qudit algorithms.