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Project produces tools and data to correct for systematic frequency shifts and enable automated validation supporting redefinition of the SI second
Advances in telecommunications and navigation technologies place increasing demands on the stability and accuracy of international reference timescales. Optical clocks offer better frequency stability and uncertainty than the currently used caesium primary frequency standards. Also a redefinition of the second, a base unit of the International System of Units (the SI), is anticipated based on the potential for orders-of-magnitude improvements to accuracy. However, most optical clocks contribute only intermittently to international timescales as human monitoring and intervention is required to achieve high uptimes. Automated data validation and correction for systematic frequency shifts is also necessary.
EMPIR project Robust Optical Clocks for International Timescales (18SIB05, ROCIT) is using optical fibre and satellite links to compare frequencies, while traceability to the present definition of the SI second is provided by absolute frequency measurements relative to caesium primary standards. The techniques and hardware being developed should lead to more reliable optical clocks. In addition, significant science and innovation impacts are expected to arise from international consistency and long-term reliability through realisation and dissemination of a new SI unit of time. For example, networks of optical clocks could be used to measure the Earth’s gravity potential with high temporal and spatial resolution via the gravitational redshift of their operating frequencies.
Project highlights so far include:
- Following approval from the CCTF Working Group on Primary and Secondary Frequency Standards, data from Italy’s National Measurement Institute’s (INRIM) ytterbium optical lattice clock appeared in BIPM publication Circular T no. 383 (November 2019) and was used for the computation of International Atomic Time.
- Software for long-term laser stabilisation has been contributed to the open source GitHub project. The stabiliser is a Computer Processing Unit (CPU) based dual-channel fast servo that is suitable for use in commercialising quantum technologies as well as in fundamental physics research.
- A paper on Long term measurement of the 87Sr clock frequency at the limit of primary Cs clocks was published in the journal Physical Review Research.
- A paper on Improved limits for violations of local position invariance from atomic clock comparisons was published in the journal Physics Review Letters.
Project Coordinator Helen Margolis from NPL said
‘The scientific and technical objectives of the ROCIT project are closely aligned with important milestones on the international roadmap towards a redefinition of the SI second. Improving the robustness of optical clocks so that they can run unattended for long periods is a key enabler for their use in international timescales, and by the end of the project we expect that several European optical clocks will be contributing on a regular basis to International Atomic Time, improving its stability and accuracy.’.
This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.
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