arXiv:2505.04854 · Physical Review A

Spontaneous Raman scattering out of a metastable atomic qubit

I. D. Moore, A. Quinn, Jameson P. O'Reilly, Jeremy Metzner, S. Brudney, G. J. Gregory, D. J. Wineland, D. T. C. Allcock

Published Aug 18, 2025• 1 citation

Abstract

Metastable qubits in atomic systems can enable large-scale quantum computing by simplifying hardware requirements and adding efficient erasure conversion to the preexisting toolbox of high-fidelity laser-based control. For trapped atomic ions, the fundamental error floor of this control is given by spontaneous Raman and Rayleigh scattering from short-lived excited states. We measure spontaneous Raman scattering rates out of a metastable ${D}_{5/2}$ qubit manifold of a single trapped $^{40}\mathrm{Ca}^{+}$ ion illuminated by 976 nm light that is $\ensuremath{-}44$ THz detuned from the dipole-allowed transition to the ${P}_{3/2}$ manifold. This supports the calculation of error rates from both types of scattering during one- and two-qubit gates on this platform, thus demonstrating that infidelities less than ${10}^{\ensuremath{-}4}$ are possible.

DOI: 10.1103/vlz1-s6zl

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arXiv:2505.04854 · Physical Review A

Spontaneous Raman scattering out of a metastable atomic qubit

I. D. Moore, A. Quinn, Jameson P. O'Reilly, Jeremy Metzner, S. Brudney, G. J. Gregory, D. J. Wineland, D. T. C. Allcock

Published Aug 18, 2025• 1 citation

arXiv HTML PDF

Abstract

{D}_{5/2}

qubit manifold of a single trapped

^{40}\mathrm{Ca}^{+}

ion illuminated by 976 nm light that is

\ensuremath{-}44

THz detuned from the dipole-allowed transition to the

{P}_{3/2}

manifold. This supports the calculation of error rates from both types of scattering during one- and two-qubit gates on this platform, thus demonstrating that infidelities less than

{10}^{\ensuremath{-}4}

are possible.

DOI: 10.1103/vlz1-s6zl

Related papers

Spontaneous Raman scattering from metastable states of Ba +

Timothy Burke, Xiaoyang Shi, Jasmine Sinanan-Singh +2 more

Quantum logic gates performed via two-photon stimulated Raman transitions in ions and atoms are fundamentally limited by spontaneous scattering errors. Recent theoretical treatment of these processes has predicted no lower bound on the scattering-induced error rate of such gates when implemented with far-detuned lasers, while also providing an extension to metastable qubits. To validate this theoretical model, we provide experimental measurements of Raman scattering rates due to near- and far-detuned lasers for initial states in the metastable ${D}_{5/2}$ level of $^{137}\mathrm{Ba}^{+}$ . The measured spontaneous Raman scattering rate is consistent with the theoretical prediction and suggests that metastable-level two-qubit gates with an error rate approximately equal to ${10}^{\ensuremath{-}4}$ are possible with laser excitation detuned by tens of terahertz or more.Quantum logic gates performed via two-photon stimulated Raman transitions in ions and atoms are fundamentally limited by spontaneous scattering errors. Recent theoretical treatment of these processes has predicted no lower bound on the scattering-induced error rate of such gates when implemented with far-detuned lasers, while also providing an extension to metastable qubits. To validate this theoretical model, we provide experimental measurements of Raman scattering rates due to near- and far-detuned lasers for initial states in the metastable ${D}_{5/2}$ level of $^{137}\mathrm{Ba}^{+}$. The measured spontaneous Raman scattering rate is consistent with the theoretical prediction and suggests that metastable-level two-qubit gates with an error rate approximately equal to ${10}^{\ensuremath{-}4}$ are possible with laser excitation detuned by tens of terahertz or more.

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arXiv:2408.00975Aug 2, 20240 citations

{D}_{5/2}

qubit manifold of a single trapped

^{40}\mathrm{Ca}^{+}

ion illuminated by 976 nm light that is

\ensuremath{-}44

THz detuned from the dipole-allowed transition to the

{P}_{3/2}

manifold. This supports the calculation of error rates from both types of scattering during one- and two-qubit gates on this platform, thus demonstrating that infidelities less than

{10}^{\ensuremath{-}4}

are possible.

{D}_{5/2}

level of

^{137}\mathrm{Ba}^{+}

. The measured spontaneous Raman scattering rate is consistent with the theoretical prediction and suggests that metastable-level two-qubit gates with an error rate approximately equal to ${10}^{\ensuremath{-}4}$ are possible with laser excitation detuned by tens of terahertz or more.

\sim 94\%

of spontaneous Raman scattering errors during logic gates and nearly all errors from qubit decay. Second, we perform a two-ion geometric phase gate using far-detuned (-44\,THz) stimulated Raman transitions to produce an entangled state with a raw Bell state fidelity of 97.73\% and a SPAM-corrected Bell state fidelity of 98.61\%. When subtracting erasure errors, this fidelity becomes 99.16\%. These results, along with projections based on our detailed error budget, demonstrate metastable trapped-ion qubits as a platform for low-overhead, fault-tolerant quantum computing.

Spontaneous Raman scattering from metastable states of Ba

^+

_{5/2}

level of

^{137}

^+

. The measured spontaneous Raman scattering rate is consistent with the theoretical prediction and suggests that metastable-level two-qubit gates with an error rate

\approx10^{-4}

are possible with laser excitation detuned by tens of terahertz or more.

{D}_{5/2}

manifold, showing that gate errors below ${10}^{\ensuremath{-}4}$ are achievable for all commonly used trapped ions.

5D_{5/2}

state of a single

^{137}

^+

ion. In agreement with a model based on empirical results from dynamical-decoupling-based noise spectroscopy, we find that dephasing of the metastable levels is the dominant source of error once erasure errors are removed.