International Timescales with Optical Clocks

The SI unit of time, the second, is currently defined in terms of the frequency of the microwave transition between the two ground state hyperfine levels of the 133Cs atom. However the most advanced optical atomic clocks have now reached levels of stability and accuracy that significantly surpass the performance of the best caesium primary standards. As a result, the possibility of a future redefinition of the second is being considered by the international metrology community.

Our project aims to tackle the key challenges that must be addressed before such a redefinition can be implemented. We will:

  • Develop improved methods for comparing optical clocks developed in different laboratories.

  • Carry out a coordinated programme of clock comparisons to validate the performance levels of the optical clocks, to anchor their frequencies as well as possible to the current definition of the second, and to establish the leading contenders for a redefinition of the second.

  • Evaluate relativistic effects influencing comparisons between clocks at an improved level of accuracy, including the gravitational redshift of the clock transition frequency.

  • Establish a framework and procedures for the optical clocks to be integrated into international timescales.

For more information, please contact the project coordinator, Dr Helen Margolis from NPL.

The research within this EURAMET joint research project receives funding from the European Community's Seventh Framework Programme, ERA-NET Plus, under Grant Agreement No. 217257.

ITOC final workshop:

The ITOC final workshop took place on Friday 8 April 2016 at the University of York, UK, in association with EFTF 2016

News article in Nature:

The 4 June 2015 edition of Nature includes a news story that discusses our experiment to compare optical clocks by broadband two-way satellite time and frequency transfer.

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