Actinide ions for testing the spatial $\alpha-$variation hypothesis

TL;DR

This paper identifies actinide ions Cf$^{15+}$ and Es$^{16+}$ as promising candidates for high-precision tests of spatial variations in the fine-structure constant, leveraging their atomic properties and potential for precise frequency measurements.

Contribution

It systematically searches for atomic systems suitable for testing spatial $eta$-variation of $ ext{alpha}$, highlighting actinide ions as optimal candidates.

Findings

Cf$^{15+}$ and Es$^{16+}$ ions are ideal for $ ext{alpha}$-variation tests.

These ions enable frequency measurements with fractional accuracy better than 10^{-18}.

The electronic structure of these ions allows for high-precision atomic property predictions.

Abstract

Testing the spatial variation of fine-structure constant $\alpha$ indicated in [Webb et al., Phys. Rev. Lett. 107, 191101 (2011)] with terrestrial laboratory atomic measurements requires at least $\dot{\alpha}/\alpha \sim 10^{-19}~\textrm{y}^{-1}$ sensitivity. We conduct a systematic search of atomic systems for such a test that have all features of the best optical clock transitions leading to possibility of the frequency measurements with fractional accuracy on the level of $10^{-18}$ or better and have a factor of 100 extra enhancement of $\alpha$-variation in comparisons to experimental frequency ratio measurement accuracy. We identify the pair of actinide Cf$^{15+}$ and Es$^{16+}$ ions as the best system for a test of spatial $\alpha-$variation hypothesis as it satisfies both of these requirements and have sufficiently simple electronic structure to allow for high-precision predictions of all atomic properties required for rapid experimental progress.