Spontaneous Raman scattering from metastable states of Ba$^+$

TL;DR

This paper experimentally measures Raman scattering rates in metastable Ba$^+$ ions, confirming theoretical predictions that enable ultra-low-error quantum gates with far-detuned lasers, advancing quantum computing technology.

Contribution

It provides the first experimental validation of theoretical models predicting no lower bound on scattering errors for metastable qubits with far-detuned lasers.

Findings

Measured Raman scattering rates match theoretical predictions.

Metastable qubits can achieve error rates around 10^{-4}.

Far-detuned lasers enable high-fidelity quantum gates.

Abstract

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 scattering processes has predicted no lower bound on the 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 $^{137}$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 $\approx10^{-4}$ are possible with laser excitation detuned by tens of terahertz or more.