A research team at the Chinese Academy of Sciences has built a second‑generation, liquid‑nitrogen‑cooled calcium‑ion optical clock whose total systematic uncertainty is 4.4×10⁻19. That fractional uncertainty, the institute says, corresponds to a timing error of less than one second over about 72 billion years — a performance the report describes as the highest uncertainty metric published to date for any optical clock.
Optical clocks measure time by counting the oscillations of light absorbed and emitted by atoms, achieving far higher frequencies and therefore greater precision than microwave atomic clocks that underpin today’s international time standard. The new device uses trapped Ca+ ions held and interrogated at low temperatures with liquid‑nitrogen cooling to suppress thermal and environmental perturbations; this combination reduces systematic frequency shifts that limit long‑term accuracy.
The practical upshot of such ultra‑precise timekeepers reaches well beyond laboratory metrology. Improved clocks enable chronometric geodesy — the ability to map differences in gravitational potential (and thus height) by measuring tiny relativistic frequency shifts — and can sharpen navigation, telecoms synchronization and financial trading systems. At a strategic level, more precise national timing capability strengthens resilience of critical infrastructure and bolsters technological sovereignty.
This advance also sits within an intense international race to push fractional uncertainties ever lower and to prepare for a possible redefinition of the second based on optical rather than microwave transitions. Different technical routes compete: single‑ion clocks, like the calcium device reported here, favour long interrogation times and low environmental susceptibility, while optical‑lattice clocks using neutral atoms trade single‑quantum stability for larger atom numbers. Both approaches are narrowing the gap toward consensus on a new time standard.
Challenges remain before laboratory records translate into widespread capability. Optical clocks are still complex, require advanced environmental control and robust frequency distribution networks to be useful at scale. The next steps for the Chinese team are likely to include long‑baseline comparisons with other leading clocks, integration into fiber and satellite timing links, and efforts to reduce size, cost and operational burden so the technology can move from national metrology institutes into commercial and defence applications.