Absolute frequency of ${}^{87}\mathrm{Sr}$ at $1.8\times 10^{-16}$ uncertainty by reference to remote Primary Frequency Standards

Nils Nemitz, Tadahiro Gotoh, Fumimaru Nakagawa +4

The optical lattice clock NICT-Sr1 regularly reports calibration measurements of the international timescale TAI. By comparing measurement results to the reports of eight Primary F…