Optical clocks for improved time scales

Accurate time scales are vital to modern life, from telecommunications and satellite-navigation to secure banking, and make up part of Europe’s critical infrastructure. Current timescales are based microwave frequency standards but, in recent years, optical frequency standards (OFS) have made great progress. In their roadmap paper, the Consultative Committee for Time and Frequency (CCFT) has highlighted the need for OFS for the redefinition of the SI second, anticipated in 2030.

OFS utilise optical transitions in trapped ions or neutral atoms held in optical lattices and are able to reach uncertainties of 10^-18, two orders of magnitude better than the best microwave standards. However, the contributions of OFS to international time scales has so far been negligible. The CCTF roadmap paper requires “regular contributions of OFS to the international atomic time scale (TAI)” but has only reached a fulfilment level of 30-50 %. CCTF recommendation CCT 24 3 calls for improved uptimes to improve OFS’ contributions to the TAI, requiring improved methodology and hardware to be developed.

This project will develop novel metrology needed for the realisation of coordinated universal time (UTC(k)) time scales using optical clocks. This includes new hardware (particularly, optical flywheel oscillators, needed to steer optical clocks) and validated methodologies to improve uncertainties. The project will also work to strengthen the continuous operation of OFS, targeting uptimes of > 90 %, and use optical fibre links to compare and validate UTC(k) time scales.

This project will improve the uncertainty and reliability of OFS, paving the way for the next generation of atomic clocks and the redefinition of the second to better protect global time scales and vital modern applications.