Long term measurement of the ${}^{87}$Sr clock frequency at the limit of primary Cs clocks

Abstract

We report on a series of 42 measurements of the transition frequency of the 429~THz (5s${}^2$)~${}^1$S${}_0$--(5s5p)~${}^3$P${}_0$ line in ${}^{87}$Sr taken over three years from 2017 to 2019. They have been performed at the Physikalisch-Technische Bundesanstalt (PTB) between the laboratory strontium lattice clock and the primary caesium fountain clocks CSF1 and CSF2. The length of each individual measurement run has been extended by use of a hydrogen maser as flywheel to improve the statistical uncertainty given by the Cs clocks. We determine an averaged transition frequency of $429228004229873.00(0.07)$~Hz with $1.5\times 10^{-16}$ fractional uncertainty, at the limit of the current realization of the unit hertz. Analysis of the data provides an improved limit on the coupling of the gravitational potential of the Sun to the proton--electron mass ratio $\mu$, and confirms the limits on its temporal drift.

8 pages, 4 figures

References in corpus (18)

• Frequency ratio of two optical clock transitions in ${}^{171}$Yb${}^{+}$ and constraints on the time-variation of fundamental constants
• Improved limit on a temporal variation of $m_p/m_e$ from comparisons of Yb${}^{+}$ and Cs atomic clocks
• New Limits on Coupling of Fundamental Constants to Gravity Using ${}^{87}$Sr Optical Lattice Clocks
• Enhanced sensitivity to variation of the fine structure constant and m_p/m_e in diatomic molecules
• ${}^{87}$Sr lattice clock with inaccuracy below 10${}^{-15}$
• The absolute frequency of the 87Sr optical clock transition
• Improved tests of Local Position Invariance using 87Rb and 133Cs fountains
• Improved frequency measurement of a one-dimensional optical lattice clock with a spin-polarized fermionic ${}^{87}$Sr isotope
• Measuring the frequency of a Sr optical lattice clock using a 120-km coherent optical transfer
• An Optical Lattice Clock with Spin-polarized 87Sr Atoms
• Direct comparison of a Ca+ single ion clock against a Sr optical lattice clock
• Strategies for reducing the light shift in atomic clocks
• Tests of local position invariance using continuously running atomic clocks
• Variation of fundamental constants: theory and observations
• The unit of time: present and future directions
• Absolute frequency measurement with uncertainty below $1\times 10^{-15}$ using International Atomic Time
• Limits on gravitational Einstein Equivalence Principle violation from monitoring atomic clock frequencies during a year
• Search for varying constants of nature from astronomical observation of molecules