We have measured the geopotential difference between two locations separated by $457~\mathrm{ km}$ by comparison of two optical lattice clocks via an interferometric fiber link, utilizing the gravitational redshift of the clock transition frequency. The $^{ 87}$Sr clocks have been compared side-by-side before and after one of the clocks was moved to the remote location. The chronometrically measured geopotential difference of $3918.1(2.6)\,\mathrm{ m^2 \, s^{ -2}}$ agrees with an independent geodetic determination of $3915.88(0.30)\,\mathrm{ m^2 \, s^{ -2}}$. The uncertainty of the chronometric geopotential difference is equivalent to an uncertainty of $27~\mathrm{ cm}$ in height.
Categories: physics.atom-ph quant-ph