# metrology

China’s Team Builds World‑Leading Optical Clock, Pushing Timekeeping to 4.4×10⁻¹⁹ Precision

A Chinese Academy of Sciences team has developed a liquid‑nitrogen‑cooled calcium‑ion optical clock with a total systematic uncertainty of 4.4×10⁻19, claimed as the best reported so far. The result advances ultra‑precise timekeeping with implications for geodesy, navigation and a prospective redefinition of the second.