Transportable optical lattice clocks and general relativity

Optical lattice clocks (OLCs) enable us to measure time and frequency with a fractional uncertainty at [Formula: see text] level, which is 2 orders of magnitude better than Cs clocks. In this paper, after briefly reviewing OLCs and the history of testing the fundamental principles of general relativity, we report our experiments of measuring the gravitational redshift between RIKEN and The University of Tokyo, and at Tokyo Skytree using transportable OLCs. We also discuss a couple of future applications of OLCs such as detecting gravitational waves in space and relativistic geodesy. The possibility of testing second-order parametrized post-Newtonian potential around the Earth is also mentioned.