Ground-state cooling and ancilla readout in a mixed ground/metastable ion crystal*

The optical-metastable-ground state (omg) architecture promises the full functionality of two-species experiments, including sympathetic cooling and non-destructive ancilla readout, without the corresponding hardware overhead. We demonstrate simultaneous control and state detection of two qubits encoded in ground (g) and metastable (m) manifolds of trapped calcium ions. We also confirm that we can cool global modes of the Coulomb crystal to the motional ground state via dissipative operations on the g qubit without disturbing the m qubit. Finally, we perform quantum logic spectroscopy to non-destructively readout the state of the m qubit using fluorescence detection of the g qubit. Extensions of these demonstrations to larger system sizes will enable the mitigation of motional heating after ion shuttling and syndrome extraction for quantum error correction, both which will be crucial for future fault-tolerant quantum computers based on trapped ions.