Atomic clock frequency ratios with fractional uncertainty $\le 3.2\times 10^{-18}$

Alexander Aeppli, Willa J. Arthur-Dworschack, Kyle Beloy +24

We report high-precision frequency ratio measurements between optical atomic clocks based on ${}^{27}$Al${}^{+}$, ${}^{171}$Yb, and ${}^{87}$Sr. With total fractional uncertainties at or bel…