Building a European optical fibre network for comparing optical atomic clocks.
Caesium atomic clocks are used to accurately define the second, the SI base unit of time. But optical atomic clocks are more accurate and more stable than caesium clocks, and are the most promising candidates for use in the proposed re-definition of the second. Clocks in different locations need to be regularly compared to reveal and reduce uncertainty, but the current satellite-based techniques used to compare caesium clocks are not precise enough. This project has built on the achievements of EMRP project SIB02 NEAT-FT and helped to unlock the full accuracy potential of optical atomic clocks, by developing comparison techniques for optical clocks based on optical fibres, including installing and upgrading fibre optic links between European National Measurement Institutes. This network will allow optical clocks to be compared at new levels of accuracy and will pave the way for future improvements in the precision of time measurement in fields such as transport, communications and finance.