Developments of optical frequency standards at NICT and all-optical comparison against a remote clock in University of Tokyo using 60km fiber link

At National Institute of Information and Communications Technology (NICT), we have lately developed a lattice clock using
⁸⁷
Sr atoms as well as a single ion clock based on
⁴⁰
Ca
⁺
. Besides the comparison of the two atomic standards inside the institute, all-optical fiber-link to transfer frequency standards to the University of Tokyo (UT) has been developed to evaluate the uncertainty and stability of our standards by referring the state-of-the-art lattice clock locating in UT. The initial evaluations have resulted in the relative stability of 10
^-16
level, clearly showing the differential frequency of 4-5Hz mainly caused by the 45m difference of the elevation.