Experimenting an optical second with strontium lattice clocks

TL;DR

This paper demonstrates the high precision comparison of strontium optical lattice clocks with cesium microwave fountains, advancing the potential for redefining the SI second based on optical transitions.

Contribution

It presents the first agreement within the accuracy budget of two state-of-the-art strontium optical lattice clocks and links optical and microwave time standards with unprecedented consistency.

Findings

Strontium optical clocks agree within 1.6x10^(-16)

Comparison with cesium fountains shows reproducibility at 3.1x10^(-16)

System connects optical and microwave time standards effectively

Abstract

Progress in realizing the SI second had multiple technological impacts and enabled to further constraint theoretical models in fundamental physics. Caesium microwave fountains, realizing best the second according to its current definition with a relative uncertainty of 2-4x10^(-16), have already been superseded by atomic clocks referenced to an optical transition, both more stable and more accurate. Are we ready for a new definition of the second? Here we present an important step in this direction: our system of five clocks connects with an unprecedented consistency the optical and the microwave worlds. For the first time, two state-of-the-art strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.6x10^(-16). Their comparison with three independent caesium fountains shows a degree of reproducibility henceforth solely limited at the level of 3.1x10^(-16) by the best realizations of the microwave-defined second.