Prospects for frequency comparison of Sr and Hg optical lattice clocks toward 10−18 uncertainties

We are developing optical lattice clocks with a scope of attaining 10^-18 fractional uncertainty. Cryogenic silicon cavity targeting 2×10^-17 stability at 1s, will allow full utilization of the potential stability of optical lattice clocks. In order to reduce the blackbody radiation shift, which is the most serious source of uncertainties, Sr clocks in cryogenic environment and Hg clocks are underdevelopment. We discuss prospects for clock comparison, no dead time operation of the clocks and fiber link of the clocks between Riken and the University of Tokyo.