Improved frequency measurement of the $^1S_{0}$-$^3P_{0}$ clock transition in $^{87}$Sr using the Cs fountain clock at NMIJ as a transfer oscillator

TL;DR

This paper reports a highly precise absolute frequency measurement of the $^1S_{0}$-$^3P_{0}$ transition in $^{87}$Sr, achieving a fractional uncertainty of 1.2×10⁻¹⁵ by using a Cs fountain clock as a transfer oscillator.

Contribution

The study introduces an improved measurement technique that significantly reduces uncertainty by employing a Cs fountain clock as a transfer oscillator for the first time in this context.

Findings

Achieved fractional uncertainty of 1.2×10⁻¹⁵ in frequency measurement.

Provided a precise value of 429 228 004 229 873.56(49) Hz for the transition.

Reduced measurement uncertainty to less than one third of previous results.

Abstract

We performed an absolute frequency measurement of the $^1S_{0}$-$^3P_{0}$ transition in $^{87}$Sr with a fractional uncertainty of $1.2 \times 10^{-15}$, which is less than one third that of our previous measurement. A caesium fountain atomic clock was used as a transfer oscillator to reduce the uncertainty of the link between a strontium optical lattice clock and the SI second. The absolute value of the transition frequency is 429 228 004 229 873.56(49) Hz.