Single-Ion Atomic Clock with $3\times10^{-18}$ Systematic Uncertainty

TL;DR

This paper demonstrates a single-ion optical clock with a systematic uncertainty of 3×10⁻¹⁸, achieved through advanced spectroscopy techniques and precise environmental shift measurements, marking a significant step in ultra-precise timekeeping.

Contribution

The study introduces a Ramsey-type excitation scheme and detailed polarizability measurements to reduce systematic uncertainties in a single-ion optical clock.

Findings

Achieved a systematic uncertainty of 3×10⁻¹⁸ in the clock.

Reduced thermal radiation shift uncertainty to 1.8×10⁻¹⁸.

Identified residual ion motion as the main uncertainty source.

Abstract

We experimentally investigate an optical frequency standard based on the $^2S_{1/2} (F=0)\to {}^2F_{7/2} (F=3)$ electric octupole (\textit{E}3) transition of a single trapped $^{171}$Yb$^+$ ion. For the spectroscopy of this strongly forbidden transition, we utilize a Ramsey-type excitation scheme that provides immunity to probe-induced frequency shifts. The cancellation of these shifts is controlled by interleaved single-pulse Rabi spectroscopy which reduces the related relative frequency uncertainty to $1.1\times 10^{-18}$. To determine the frequency shift due to thermal radiation emitted by the ion's environment, we measure the static scalar differential polarizability of the \textit{E}3 transition as $0.888(16)\times 10^{-40}$ J m$^2$/V$^2$ and a dynamic correction $\eta(300~\text{K})=-0.0015(7)$. This reduces the uncertainty due to thermal radiation to $1.8\times 10^{-18}$. The residual motion of the ion yields the largest contribution $(2.1\times 10^{-18})$ to the total systematic relative uncertainty of the clock of $3.2\times 10^{-18}$.