Improvements of an 171Yb optical lattice clock at KRISS

The development of an Yb optical lattice clock at the Korea Research Institute of Standards and Science (KRISS) is reported with current systematic uncertainty of 2.9×10^-16. A highly stable clock laser at 578 nm was developed with a short-term linewidth of 3.5 Hz. The laser was locked to the clock transition and the fractional frequency stability was 2.0×10^-15 at 1s. Collisional frequency shift for Rabi spectroscopy was theoretically and experimentally investigated and the uncertainty was greatly reduced to 2.9×10^-17. We identified conditions to further reduce the collisional shift uncertainty to 10^-18 level.