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.