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Roadmap towards the redefinition of the second



C Rieck, T Ido, M Wouters, Y Hanado, M Fujieda, PO Hedekvist, PE Pottie, J Bartholomew, J Hanssen, A Malimon, N Ashby, P Defraigne, Elizabeth Donley, I Sesia, H Schnatz, P Dube, N Dimarc, F Levi, H Margolis, S Slyusarev, M Yasuda, S Bize, D Calonico, David B. Newell, JP Uzan, M Gertsvolf, C Oates, E Peik, S Weyers, DH Yu, G Mileti, P Tavella, F Meynadier, G Petit, G Panfilo, F Fang, J Lodewyck


This paper outlines the roadmap towards the redefinition of the second recently updated by the CCTF Task Force created by the CCTF in 2020. The main achievements and the open challenges related to the status of the optical frequency standards, their contribution to time scales and UTC, the possibility of their comparison and the knowledge of the Earth gravitational potential at the necessary level of uncertainty are discussed. Also, the mandatory criteria to be achieved before redefinition and their current fulfillment level, together with the redefinition options based on a single or on a set of transitions are described.


Time and Frequency Metrology, Optical Clocks, Redefinition, International System of Units


Rieck, C. , Ido, T. , Wouters, M. , Hanado, Y. , Fujieda, M. , Hedekvist, P. , Pottie, P. , Bartholomew, J. , Hanssen, J. , Malimon, A. , Ashby, N. , Defraigne, P. , Donley, E. , Sesia, I. , Schnatz, H. , Dube, P. , Dimarc, N. , Levi, F. , Margolis, H. , Slyusarev, S. , Yasuda, M. , Bize, S. , Calonico, D. , Newell, D. , Uzan, J. , Gertsvolf, M. , Oates, C. , Peik, E. , Weyers, S. , Yu, D. , Mileti, G. , Tavella, P. , Meynadier, F. , Petit, G. , Panfilo, G. , Fang, F. and Lodewyck, J. (2024), Roadmap towards the redefinition of the second, Metrologia, [online],, (Accessed May 19, 2024)


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Created January 22, 2024, Updated April 4, 2024