Prospects of a Pb$^{2+}$ ion clock

TL;DR

This paper proposes a highly stable atomic clock based on a specific transition in doubly ionized lead, which is immune to many common perturbations and suitable for precise timekeeping.

Contribution

It introduces a novel lead ion clock design utilizing a transition immune to nonscalar perturbations and discusses its practical advantages for high-precision time measurement.

Findings

Clock states are nondegenerate and immune to Zeeman and quadrupole shifts.

The proposed clock is resistant to blackbody radiation, Doppler, and second order Zeeman shifts.

Two-photon E1+M1 transition allows manageable Stark shifts for practical operation.

Abstract

We propose a high-performance atomic clock based on the 1.81 PHz transition between the ground and first-excited state of doubly ionized lead. Utilizing an even isotope of lead, both clock states have $I=J=F=0$, where $I$, $J$, and $F$ are the conventional quantum numbers specifying nuclear, electronic, and total angular momentum, respectively. The clock states are nondegenerate and completely immune to nonscalar perturbations, including first order Zeeman and electric quadrupole shifts. Additionally, the proposed clock is relatively insusceptible to other frequency shifts (blackbody radiation, second order Zeeman, Doppler), accommodates "magic" rf trapping, and is robust against decoherence mechanisms that can otherwise limit clock stability. By driving the transition as a two-photon $E1$+$M1$ process, the accompanying probe Stark shift is appreciable yet manageable for practical Rabi frequencies.