171Yb+ optical clock with 2.2×10−18 systematic uncertainty and absolute frequency measurements

Abstract

A full evaluation of the uncertainty budget for the ytterbium ion optical clock at the National Physical Laboratory (NPL) was performed on the electric octupole (E3) 2S1/2→2F7/2 transition. The total systematic frequency shift was measured with a fractional standard systematic uncertainty of 2.2×10−18 . Furthermore, the absolute frequency of the E3 transition of the 171Yb+ ion was measured between 2019 and 2023 via a link to International Atomic Time (TAI) and against the local caesium fountain NPL-CsF2. The absolute frequencies were measured with fractional standard uncertainties between 3.7×10−16 and 1.1×10−15 , and all were in agreement with the 2021 BIPM recommended frequency.