# Raman gates in metastable trapped-ion qubits

# Raman gates in metastable trapped-ion qubits

Trapped ions are currently a leading platform for quantum computing (QC), and techniques for controlling them at high enough fidelities and in large enough numbers to perform useful, fault-tolerant QC are an active research area. One proposed scheme for implementing trapped-ion QC uses different electronic state transitions to encode different types of quantum bits (qubits) which can be controlled with low between-type cross-talk [1]. A type of qubit that this scheme would rely on, but which has not been widely studied, is the metastable (m) qubit, encoded in long-lived metastable excited states. In our lab, we have implemented m qubits in the D5/2 manifold of 40Ca+ and performed single- and two-qubit Raman gates, carrying out one of the first entangling gates recorded in m qubits and achieving Bell state fidelities of 97(1)%. To perform these gates, we use infrared Raman beams tuned 44 THz red of the 854 nm P3/2 <-> D5/2 transition, allowing us to achieve low spontaneous Raman scattering errors. We have measured the Raman scattering rate from these beams, and comparing these results to scattering models that account for effects relevant at far detunings [2], we find that error rates from Raman scattering at this wavelength can be made low enough that they are no longer a limiting factor in achieving fidelities needed for fault-tolerance.