Overview
- USTC reports uncertainty of 9.2×10^-19 and fractional-frequency stability of 6.3×10^-19, implying drift under a second over roughly 30 billion years.
- The result, published in Metrologia, upgrades a strontium optical lattice clock that measures seconds at visible‑light frequencies.
- Redefinition requires reproducible performance from at least three clocks using the same atomic transition at different labs; two other strontium systems and two aluminium‑ion clocks have already met comparable marks.
- The CGPM will not decide a new definition at its October 2026 meeting, with a formal proposal now expected to be prepared for the 29th CGPM in 2030.
- Sub‑10^-18 timekeeping could enable millimetre‑scale relativistic geodesy, tighter dark‑matter searches, and finer monitoring of crustal, groundwater, and volcanic changes.