Optical Lattice Clocks as Candidates for a Possible Redefinition of the SI Second

In this paper, we review several characteristics of optical lattice clocks as candidates for a future redefinition of the International System of Units (SI) second using an atomic transition in the optical domain, focusing on experiments performed at SYRTE using one mercury (Hg) and two strontium (Sr) optical lattice clocks. Beyond the technical aspects such as the stability and systematic frequency-shift assessments of the clocks, practical aspects have to be considered, such as the careful determination of the optical frequency with respect to the cesium primary standard and the worldwide reproducibility of the clock frequency by local and remote clock comparisons.