Raman scattering errors in hyperfine trapped-ion qubits and implementation of Raman gates in the metastable state

Characterization of single and two qubit gates in metastable states (m qubits) is essential for realizing the omg scheme, which would allow for multi-species functionality with a single ion species [1]. We present an implementation of m qubits in the D^5/2 manifold of 40Ca⁺. Single-qubit Raman gates in m qubits are demonstrated and characterized. We use 976 nm Raman beams (tuned 44 THz red of the 854 nm P^3/2 <-> D^5/2 transition) in order to achieve low spontaneous Raman scattering errors. We compare these observed scattering errors to theory, accounting for effects relevant at large detunings and we present experimental progress towards implementing a two qubit Mølmer-Sørensen gate using the far-detuned Raman beams. We also consider these effects in models for Raman scattering in qubits in the S^1/2 manifold (g qubits) and predict markedly different scattering behavior [2] in the far-detuned regime than previous models.

[1] D. T. C. Allcock et al., omg Blueprint for trapped ion quantum computing with metastable states, Applied Physics Letters 119, 214002 (2021)

[2] I. D. Moore et al., “Photon scattering errors during stimulated Raman transitions in trapped-ion qubits”, 2022; [http://arxiv.org/abs/2211.00744 arXiv:2211.00744].