Trapped-Ion Quantum Information with Metastable Qubits*

Most quantum information experiments with trapped ions rely on encoding the qubit in two Zeeman or hyperfine sublevels of the ground electronic state or between the ground state and a long-lived metastable state. We report work investigating another category of qubits: the metastable qubit, in which the qubit is encoded in sublevels of a long-lived metastable state. Qubits in this metastable manifold would be largely insensitive to scattered laser light addressing a neighboring qubit in the ground state manifold and vice versa. This could enable quasi-dual species operation, in which many of the applications of dual-species ion trapping, such as sympathetic cooling or ancilla qubits in quantum error correcting codes, could be implemented in a chain of identical ions. This would improve the vibrational mode structure and potentially reduce experimental complexity. We present experimental progress towards metastable qubit operations using ⁸⁸Sr⁺ and ¹³³Ba⁺ ions, which have accessible visible and infrared transition wavelengths and an appropriate atomic structure for encoding quantum information in a metastable qubit.