Low-lying $D$ states in yttrium and actinium ions highly sensitive to variation of the fine structure constant

Akio Kawasaki

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arXiv · 2606.29676

Low-lying $D$ states in yttrium and actinium ions highly sensitive to variation of the fine structure constant

Akio Kawasaki

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Abstract

Whether fundamental constants vary over time or space is one of the key questions in metrology and cosmology. Among them, variation of the fine structure constant $\alpha$ is intensively investigated. Yttrium ions Y$^+$ and actinium ions Ac$^+$ have low-lying $D$ states that are suitable for this search, with a proper path for laser cooling and detection. Theoretical calculations show that the sensitivities of the transitions between the ground state and the lowest $^3D_1$ states are $K=9.40$ and $K=9.73$, respectively. By driving the transition between the ground state and the $^3D_1$ states with a two-photon transition, the transition can be used for a high-sensitivity search for time variation of the fine structure constant. The high efficiency of a detection scheme using the transition between the $7s6d~^3D_1$ states and the $7s7p~^3P_0$ state also suggests that Ac$^+$ ions are potentially useful as a platform for quantum information processing.

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Akio Kawasaki. 2026-06-29. Low-lying $D$ states in yttrium and actinium ions highly sensitive to variation of the fine structure constant. https://arxiv.org/abs/2606.29676

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