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Reevaluation of the primary fountain clocks


Based on latest findings the primary caesium fountain clocks of PTB, CSF1 and CSF2, were again investigated with regard to frequency shifting effects [1]. New techniques for sensitive detection and suppression of frequency shifts have been developed and applied. As a result the relative frequency uncertainties have been reduced to 2.7×10-16 and 1.7×10-16 for CSF1 and CSF2, respectively. Both clocks thus belong to the few top ranking fountain clocks around the world.

CSF1 and CSF2 are utilized for steering the international atomic timescale TAI and the national atomic time scale UTC(PTB), which is the basis for German legal time. Other important applications are absolute frequency measurements of optical clocks as a step towards a redefinition of the second and investigations in the field of fundamental physics, such as the question about temporal variations of fundamental constants.

[1] S. Weyers, V. Gerginov, M. Kazda, J. Rahm, B. Lipphardt, G. Dobrev and K. Gibble, Advances in the accuracy, stability, and reliability of the PTB primary fountain clocks, Metrologia 55(6), 789–805 (2018)