Hf12+ ion: Highly charged ion for next-generation atomic clocks and tests of fundamental physics

Abstract

We use advanced computational techniques to study the electronic structure of the Hf${}^{12+}$ ion, with the goal of assessing its potential for use in highly accurate atomic optical clocks and in the search for new physics. Such clocks should combine low sensitivity to external perturbations with high sensitivity to a possible time variation of the fine-structure constant $\alpha$. The system features two clock transitions. One is an $f-p$ transition in terms of single-electron states, which exhibits strong sensitivity to variations in $\alpha$. The other is an electric-quadrupole (E2) transition between states of the ground-state configuration, which can serve as an anchor transition for measuring one frequency against the other.

All three relevant states possess very small and nearly equal static dipole polarizabilities, resulting in an extremely small blackbody-radiation shift. The quadrupole shift is also small and can be further suppressed. Altogether, Hf${}^{12+}$ appears to be a highly promising candidate for both precision timekeeping and searches for new physics.