A strontium optical lattice clock with $1 \times 10^{-17}$ uncertainty and measurement of its absolute frequency

TL;DR

This paper reports a highly precise measurement of the strontium optical lattice clock's absolute frequency, achieving a fractional uncertainty of 1×10⁻¹⁷, and details its systematic evaluation and traceability to SI units.

Contribution

It provides the first detailed evaluation of systematic shifts for a strontium lattice clock at 10⁻¹⁷ uncertainty and links the measurement to TAI with high accuracy.

Findings

Absolute frequency measured as 429228004229873.1(5) Hz

Total systematic uncertainty of 1×10⁻¹⁷

Agreement with other global measurements

Abstract

We present a measurement of the absolute frequency of the 5s$^2$ $^1$S$_0$ to 5s5p $^3$P$_0$ transition in $^{87}$Sr, which is a secondary representation of the SI second. We describe the optical lattice clock apparatus used for the measurement, and we focus in detail on how its systematic frequency shifts are evaluated with a total fractional uncertainty of $1 \times 10^{-17}$. Traceability to the International System of Units is provided via comparison to International Atomic Time (TAI). Gathering data over 5- and 15-day periods, with the lattice clock operating on average 74$\%$ of the time, we measure the frequency of the transition to be 429228004229873.1(5) Hz, which corresponds to a fractional uncertainty of $1 \times 10^{-15}$. We describe in detail how this uncertainty arises from the intermediate steps linking the optical frequency standard, through our local time scale UTC(NPL), to an ensemble of primary and secondary frequency standards which steer TAI. The calculated absolute frequency of the transition is in good agreement with recent measurements carried out in other laboratories around the world.