Optical atomic clocks–what challenges remain on the roadmap towards a redefinition of the SI second?

Helen Margolis
NPL (UK)
ICAP2022
Wednesday, Jul 20, 3:50 PM

Optical atomic clocks – what challenges remain on the roadmap towards a redefinition of the SI second?

Over recent years, there has been enormous progress in the development of optical atomic clocks based on either atoms trapped in an optical lattice or single trapped ions. These optical clocks have demonstrated unprecedented frequency stability and estimated systematic frequency uncertainty, far surpassing the current generation of caesium microwave primary frequency standards, with the result that a future optical redefinition of the SI second is anticipated. However before this can happen several key challenges remain to be addressed.

First of all, the uncertainty budgets of the optical clocks need to be validated through a programme of international comparisons between systems developed independently by different research groups around the world. Continuity with the current caesium-based definition must also be ensured, by performing absolute frequency measurements with as low an uncertainty as possible. And finally, we need to improve the robustness of optical clocks and automate their operation, enabling them to be operated routinely as secondary representations of the second, regularly contributing to International Atomic Time (TAI) via reporting to the International Bureau of Weights and Measures, and being used to steer the local UTC(k) time scales maintained by national timing laboratories. I will discuss recent progress towards addressing these challenges, in particular drawing on examples of NPL work performed in the European collaborative project Robust Optical Clocks for International Timescales (ROCIT).