Sr lattice clock at 1x10^{-16} fractional uncertainty by remote optical evaluation with a Ca clock

TL;DR

This paper demonstrates a remote optical clock comparison over urban distances, achieving a fractional uncertainty of 1x10^{-16} with a Sr lattice clock, surpassing cesium standards, and discusses key limiting factors.

Contribution

It presents the first high-precision remote comparison of optical clocks over km-scale distances, evaluating a Sr lattice clock at unprecedented fractional uncertainty.

Findings

Achieved 1x10^{-16} fractional uncertainty in Sr lattice clock

Performed remote clock comparison over km-scale urban distances

Identified blackbody radiation shifts as a current limiting factor

Abstract

Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies. Rigorous evaluations of these clocks require direct comparisons between them. We have realized a high-performance remote comparison of optical clocks over km-scale urban distances, a key step for development, dissemination, and application of these optical standards. Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1x10-16 fractional level, surpassing the best current evaluations of cesium (Cs) primary standards. We also report on the observation of density-dependent effects in the spin-polarized fermionic sample and discuss the current limiting effect of blackbody radiation-induced frequency shifts.