Advancing the roadmap criteria for the redefinition of the second

Caesium atomic clocks currently define the SI second and the time and frequency (T&F) signals these generate underpin the internet, energy grids, transportation and financial transactions. Other atomic clocks, such as Hydrogen Masers, are based onboard orbiting satellites and contribute to International Atomic Time (TAI). The signals from these clocks are corrected by reference to highly accurate ground-based clocks held at National Metrology Institutes (NMIs). In the last few decades, optical atomic clocks have demonstrated the ability to surpass the accuracy and stability of caesium and other atomic clocks, and in 2020 the Consultative Committee for Time and Frequency (CCTF) published a roadmap of the advances required to use optical clocks to redefine the SI second by 2030. This included the development of higher-accuracy optical clocks, their regular contribution to international time scales, and the sustainability of clock comparisons.

Building on the work of EURAMET projects such as OC18, ROCIT, TOCK, CoCoRICO  and HIOC this project will improve optical clocks to the uncertainty required by the CCFT Roadmap (<2×10^-18). New clock types will be developed and investigated and the optical fibres that carry T&F signals from NMIs will be extended to cover 7 countries. This fibre network will then be used to carry out clock campaigns at different scales to resolve the inconsistencies identified in previous studies.

The work of Arcsecond is expected to bring benefits to a wide range of sectors including telecommunication, energy distribution, new tests in fundamental physics, dark matter detection, geodesy, and quantum technologies.