Direct Comparison of Distant Optical Lattice Clocks at the $10^{-16}$ Uncertainty

TL;DR

This paper demonstrates a fiber-based method for comparing distant optical lattice clocks with a fractional uncertainty of about 10^{-16}, significantly improving the speed and accuracy of clock comparisons, which is crucial for redefining the second.

Contribution

It introduces a fiber-based remote comparison technique for optical lattice clocks with unprecedented speed and precision, surpassing satellite link methods.

Findings

Comparison instability reaches 5×10^{-16} over 1000 s

Residual fractional difference is (1.0±7.3)×10^{-16}

Method confirms clock coincidence at 10^{-16} level

Abstract

Fiber-based remote comparison of $^{87}$Sr lattice clocks in 24 km distant laboratories is demonstrated. The instability of the comparison reaches $5\times10^{-16}$ over an averaging time of 1000 s, which is two orders of magnitude shorter than that of conventional satellite links and is limited by the instabilities of the optical clocks. By correcting the systematic shifts that are predominated by the differential gravitational redshift, the residual fractional difference is found to be $(1.0\pm7.3)\times10^{-16}$, confirming the coincidence between the two clocks. The accurate and speedy comparison of distant optical clocks paves the way for a future optical redefinition of the second.