New Limits on Coupling of Fundamental Constants to Gravity Using $^{87}$Sr Optical Lattice Clocks

TL;DR

This study uses highly precise $^{87}$Sr optical lattice clocks, combined with other atomic clocks, to set new limits on how fundamental constants might vary with gravity, testing local position invariance.

Contribution

It provides the strongest limits to date on gravitational coupling coefficients for fundamental constants using $^{87}$Sr clocks and enhances constraints on their yearly drifts.

Findings

Established the best agreement on $^{87}$Sr clock frequency at 1×10^{-15}

Set new limits on gravitational coupling coefficients for $eta$, $eta_ ext{Q}$, and $eta_ ext{q}$

Improved constraints on yearly drifts of $ ext{α}$ and $ ext{μ}$

Abstract

The $^1\mathrm{S}_0$-$^3\mathrm{P}_0$ clock transition frequency $\nu_\text{Sr}$ in neutral $^{87}$Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the $1\times 10^{-15}$ level makes $\nu_\text{Sr}$ the best agreed-upon optical atomic frequency. We combine periodic variations in the $^{87}$Sr clock frequency with $^{199}$Hg$^+$ and H-maser data to test Local Position Invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant $\alpha$, electron-proton mass ratio $\mu$ and light quark mass. Furthermore, after $^{199}$Hg$^+$, $^{171}$Yb$^+$ and H, we add $^{87}$Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of $\alpha$ and $\mu$.