Four Nations Synchronize Ultra-Precise Optical Clocks

Seven ultra-precise optical clocks located in four European nations have been synchronized to an unprecedented level of accuracy, achieving agreement within 100 attoseconds. This groundbreaking achievement, detailed in a study published online on September 4, 2026, in the journal Nature, utilized signals transmitted over a dedicated fiber-optic cable network to compare the timekeeping devices. The experiment involved clocks situated in Germany, France, Italy, and Switzerland, marking a significant advancement in the field of metrology and fundamental physics.

Optical clocks represent the most accurate timekeeping devices ever created, measuring time by counting the oscillations of atoms when they transition between two specific energy levels. These transitions occur at optical frequencies, which are significantly higher than the microwave frequencies used by traditional atomic clocks, allowing for a much finer resolution in time measurement. The precision achieved in this experiment, measured in attoseconds (an attosecond is one quintillionth of a second), means that the clocks agree to within a tiny fraction of a second over extended periods, far surpassing the accuracy of any previous intercontinental clock comparisons.

The synchronization was facilitated by a specialized fiber-optic network that minimized signal degradation and latency. This network allowed researchers to send light signals between the geographically dispersed clocks and compare their readings in real-time. The ability to synchronize these highly sensitive instruments over long distances is crucial for a variety of scientific applications. These include testing fundamental physics theories, such as Einstein's theory of general relativity, which predicts that gravity affects the passage of time. By comparing clocks at different altitudes, scientists can verify these predictions with greater accuracy.

Furthermore, the synchronized clocks lay the groundwork for future advancements in global navigation satellite systems (GNSS), potentially leading to more precise positioning services. They are also essential for distributed quantum computing and advanced scientific experiments that require highly stable and synchronized time references. The successful demonstration of this attosecond-level synchronization across multiple countries highlights the maturity of optical clock technology and the robustness of the underlying fiber-optic infrastructure. This collaborative effort, involving institutions across Europe, underscores the international commitment to pushing the boundaries of scientific measurement and understanding.