Trapped-Ion Quantum Information with Metastable Qubits

S. L. Todaro | K. DeBry | X. Shi | S. B. Alterman | F. W. Knollmann | T. McCourt | G. Mintzer | J. Sinanan-Singh | C. D. Bruzewicz | J. Chiaverini | I. L. Chuang

Most quantum information experiments with trapped ions encode the qubit either between two Zeeman or hyperfine sublevels of the ground electronic state or between the ground state and a long-lived metastable state. A third category is the metastable qubit, in which quantum information is encoded in sublevels of the metastable state. Qubits in this manifold would be largely insensitive to scattered laser light addressing a neighboring qubit in the ground state manifold, potentially enabling quasi-dual-species operation in a chain of identical ions. Barium-133 ions have accessible visible and infrared transition wavelengths, hyperfine sublevels, and a metastable state with a 26 second lifetime, making them appealing for this application. However, this isotope is radioactive, with a 10.5-year half-life. We characterize the production of neutral and ionic barium by laser ablation, which could enable isotope-selective loading of barium ions into ion traps from a small radioactive source. We simultaneously present preliminary experimental investigations of a metastable qubit encoded in Zeeman sublevels of the D5/2 state of calcium-40 ions (which have a less favorable electronic structure but can be readily trapped) using a combination of lasers and RF fields.

Funding Sources: Army Research Office | Intelligence Community Postdoctoral Fellowship (S.L. Todaro) | Doc Bedard Fellowship (K. DeBry) | Laboratory for Physical Sciences (K. DeBry)