Absolute frequency measurement of the ${}^2$S${}_{1/2}{\to }^2$F${}_{7/2}$ optical clock transition in ${}^{171}$Yb${}^{+}$ with an uncertainty of $4\times 10^{-16}$ using a frequency link to International Atomic Time

Charles F. A. Baynham, Rachel M. Godun, Jonathan M. Jones +8

The highly forbidden ${}^2$S${}_{1/2}{\to }^2$F${}_{7/2}$ electric octupole transition in ${}^{171}$Yb${}^{+}$ is a potential candidate for a redefinition of the SI second. We present a…