Highly Charged Ions as a Basis of Optical Atomic Clockwork of Exceptional Accuracy

We propose a novel class of atomic clocks based on highly charged ions. We consider highly forbidden laser-accessible transitions within the $4f^{12}$ ground-state configurations of highly charged ions. Our evaluation of systematic effects demonstrates that these transitions may be used for building exceptionally accurate atomic clocks which may compete in accuracy with recently proposed nuclear clocks.

Figure 1

Systematic trend of basic clock properties for the $[\mathrm{Pd}]4f^{12}$ isoelectronic sequence. Clock frequencies (lower panel) and the ratios of radiative linewidth to the clock frequency (upper panel) are shown as a function of ionic charge. Clock frequencies lie in laser-accessible near-infrared and optical domains, while the narrow transition width assures high quality factor.

Figure 2

Proposed virtual clock transitions in ${}^{209}\mathrm{Bi}^{25+}$ highly charged ion. Averaging over the two indicated transition frequencies removes the first-order Zeeman shift. Specific choice of hyperfine components and magnetic substates minimizes shifts due to couplings to gradients of the trapping electric field.

Figure 3

Differential quadrupole moment $\Delta Q$ as a function of magnetic quantum number of the excited clock level for ${}^{209}\mathrm{Bi}^{25+}$. Different curves are labeled by values of the total angular momentum of the excited state $F$. The ground state hyperfine component remains fixed $|F_g=13/2,M_g=9/2⟩$. The minimal value of $\Delta Q$ is encircled; it is attained for the $|F_e=17/2,M_e=\pm 5/2⟩$ magic state.