Stimulated-Raman 2-qubit logic gates in metastable trapped-ion qubits

A proposed scheme for implementing trapped-ion quantum computing encodes qubits in different types of electronic levels where logic gates can be implemented with low cross-talk [1]. One type of qubit this scheme employs is the metastable (m) qubit, which has not been widely studied. We have implemented m qubits in the D_5/2 manifold of ⁴⁰Ca⁺ and performed one- and two-qubit stimulated-Raman gates, one of the first entangling gates performed in m qubits. We perform these gates using laser beams tuned 44 THz red of the 854 nm D_5/2 to P_3/2 transition. We have measured the spontaneous-Raman scattering rate from these beams, and comparing these results to scattering models we’ve developed that account for effects relevant at large detunings [2], we find that spontaneous-Raman scattering error rates at this wavelength can be made low enough that they are no longer a limiting factor in achieving fidelities needed for fault-tolerance.

[1] D. T. C. Allcock et al., Appl. Phys. Lett. 119, 214002 (2021)

[2] I. D. Moore et al., Phys. Rev. A 107, 032413 (2023)