Frequency ratio of Yb and Sr clocks with $5 \times 10^{-17}$ uncertainty at 150 s averaging time

TL;DR

This paper reports a highly precise measurement of the frequency ratio between Ytterbium and Strontium optical clocks, achieving a fractional uncertainty of 4.6×10⁻¹⁷ with significantly reduced averaging time, advancing the accuracy of fundamental frequency comparisons.

Contribution

The study demonstrates a 90-fold reduction in averaging time for frequency ratio measurements by using high-stability optical lattice clocks, improving precision over previous single-ion clock comparisons.

Findings

Achieved a fractional uncertainty of 4.6×10⁻¹⁷ in Yb/Sr frequency ratio.

Reduced averaging time by a factor of 90 compared to previous measurements.

Measured the ratio as R = 1.207507039343337749(55).

Abstract

Transition frequencies of atoms and ions are among the most accurately accessible quantities in nature, playing important roles in pushing the frontiers of science by testing fundamental laws of physics, in addition to a wide range of applications such as satellite navigation systems. Atomic clocks based on optical transitions approach uncertainties of $10^{-18}$, where full frequency descriptions are far beyond the reach of the SI second. Frequency ratios of such super clocks, on the other hand, are not subject to this limitation. They can therefore verify consistency and overall accuracy for an ensemble of super clocks, an essential step towards a redefinition of the second. However, with the measurement stabilities so far reported for such frequency ratios, a confirmation to $1 \times 10^{-18}$ uncertainty would require an averaging time $\tau$ of multiple months. Here we report a measurement of the frequency ratio of neutral ytterbium and strontium clocks with a much improved stability of $4 \times 10^{-16} ({\tau}/s)^{-1/2}$. Enabled by the high stability of optical lattice clocks interrogating hundreds of atoms, this marks a 90-fold reduction in the required averaging time over a previous record-setting experiment that determined the ratio of Al+ and Hg+ single-ion clocks to an uncertainty of $5.2 \times 10^{-17}$. For the Yb/Sr ratio, we find R = 1.207 507 039 343 337 749(55), with a fractional uncertainty of $4.6 \times 10^{-17}$.