Cryogenic optical lattice clocks with a relative frequency difference of $1\times 10^{-18}$

TL;DR

This paper demonstrates cryogenic optical lattice clocks with $^{87}$Sr atoms achieving a relative frequency difference of $1\times 10^{-18}$, addressing blackbody radiation shifts and enabling high-precision timekeeping.

Contribution

The work introduces cryogenic environment techniques for optical lattice clocks, significantly reducing uncertainties and demonstrating unprecedented accuracy and stability.

Findings

Achieved $2\times 10^{-18}$ uncertainty in two hours of operation.

Cryo-clocks agree within $(-1.1\pm 1.6)\times 10^{-18}$ after a month.

Demonstrated potential for relativistic geodesy applications.

Abstract

Time and frequency are the most accurately measurable quantities, providing foundations for science and modern technologies. The accuracy relies on the SI (Syst\'eme International) second that refers to Cs microwave clocks with fractional uncertainties at $10^{-16}$. Recent revolutionary progress of optical clocks aims to achieve $1\times 10^{-18}$ uncertainty, which however has been hindered by long averaging-times or by systematic uncertainties. Here, we demonstrate optical lattice clocks with $^{87}$Sr atoms interrogated in a cryogenic environment to address the blackbody radiation-induced frequency-shift, which remains the primary source of clocks' uncertainties and has initiated vigorous theoretical and experimental investigations. The quantum-limited stability for $N \sim 1,000$ atoms allows investigation of the uncertainties at $2\times 10^{-18}$ in two hours of clock operation. After 11 measurements performed over a month, the two cryo-clocks agree to within $(-1.1\pm 1.6)\times 10^{-18}$. Besides its contribution to fundamental science and the redefinition of the SI second, such a speedy comparison of accurate clocks provides a means for relativistic geodesy.