Transportable Strontium Optical Lattice Clocks Operated Outside Laboratory At The Level Of 10(-18) Uncertainty

Transportable strontium optical lattice clocks are developed with a fractional uncertainty of 5.5 x 10(-18) for applications outside laboratories. A single clock consists of a spectroscopy chamber and two laser boxes, where all lasers are based on external cavity diode lasers with an adjustment-free, laser-welded output coupler. When this system is transported from the laboratory at RIKEN to a broadcasting tower, the instruments experience acceleration change of 4 G at maximum. However, no serious optical misalignments are found. The demonstration opens up field applications of optical atomic clocks resolving a centimeter height difference.