Journal
METROLOGIA
Volume 51, Issue 1, Pages 108-120Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0026-1394/51/1/108
Keywords
secondary representation of the SI second; secondary and primary frequency standard; international atomic time; Rb atomic fountain
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Funding
- Laboratoire National de Metrologie et d'Essais (LNE)
- Centre National de la Recherche Scientifique (CNRS)
- Universite Pierre et Marie Curie (UPMC)
- Observatoire de Paris
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We report the first contribution to international atomic time (TAI) based on a secondary representation of the SI second. This work is done with the LNE-SYRTE FO2-Rb fountain frequency standard using the Rb-87 ground-state hyperfine transition. We describe FO2-Rb and how it is connected to local and international time scales. We report on local measurements of this frequency standard in the SI system, i.e. against primary frequency standards (PFSs), down to a fractional uncertainty of 4.4 x 10(-16), and on the establishment of the recommended value for the Rb-87 hyperfine transition by the CIPM. We also report on the process that led to the participation of the FO2-Rb frequency standard in Circular T and to the elaboration of TAI. This participation enables us to demonstrate absolute frequency measurement directly in terms of the SI second realized by the TAI ensemble with a statistical uncertainty of 1.1 x 10(-16), therefore at the limit allowed by the accuracy of PFSs. This work constitutes a demonstration of how other secondary representations, based on optical transitions, could also be used for TAI, and an investigation of a number of issues relevant to a future redefinition of the SI second.
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