Level Systematic Uncertainty*

We give updates on the characterization of the transportable ytterbium (Yb) optical lattice clock at NIST towards low 10^-18 systematic uncertainty in a rack-mounted low SWaP (size, weight, and power) form. Our current efforts focus on reducing lattice light and blackbody radiation shifts to the low 10^-18. We report efforts to demonstrate clock reproducibility after transportation to a remote site by comparison with the NIST stationary Yb clock through a 3km optical fiber link. Moreover, we are actively developing a novel stretched cubic optical cavity and a portable 1156 clock laser system with a goal of 10^-16 at 1 second instability. Demonstrating our portable clock performance at the low 10^-18 uncertainty paves way for forthcoming plans on using it in relativistic geodesy and improved tests of the general relativistic redshift.