Contributing to TAI with a secondary representation of the SI second

Abstract

Abstract-We report the first contribution to the 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 87 Rb 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, down to a fractional uncertainty of 4.4 × 10 −16 , and on the establishment of the recommended value for the 87 Rb hyperfine transition by the CIPM. We also report on the process that led to the participation of the FO2-Rb frequency standard to 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 × 10 −16 , therefore at the limit allowed by the accuracy of primary frequency standards. 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.

Atomic fountains and optical clocks at SYRTE: Status and perspectives

“…This can be done with a statistical uncertainty of 1 part in 10 −16 , and therefore at the accuracy limit of primary frequency standards defining the scale interval of TAI [57]. This illustrates how TAI provides worldwide access to the accuracy of Cs fountains.…”

“…Following this submission, the BIPM and the Working Group defined how frequency standards based on Secondary Representations will be handled by the BIPM and how they will be included into the Circular T. The Working Group was renamed Working Group on Primary and Secondary Frequency Standards and it was decided that calibrations produced by LNE-SYRTE with FO2-Rb could be included into Circular T and, since July 2013, contribute to steering TAI. This was the first time that a transition other than the Cs hyperfine transition was used to steer TAI [57].…”

Untitled

“…Atomic clocks have been generally used for timing applications [1][2][3][4] , precise tests of fundamental symmetries [5,6] , searching dark matters [7,8] , and quantum information science [9,10] . Cesium fountains have been contributing to International Atomic Time (TAI) as the most accurate primary frequency standards for more than a decade [11,12] , and rubidium fountains have been accepted as a secondary standard [1,3] .…”

“…Cesium fountains have been contributing to International Atomic Time (TAI) as the most accurate primary frequency standards for more than a decade [11,12] , and rubidium fountains have been accepted as a secondary standard [1,3] . To date, atomic fountain clocks (AFCs) have achieved a low 1 × 10 −16 level of total uncertainties and long-term stability of a low 1 × 10 −16 even to the 1 × 10 −17 level [1][2][3][4] . Optical lattice clocks and ion clocks progress rapidly, and now have achieved lower systematic uncertainty and stability of the 1 × 10 −18 level [13][14][15][16][17][18][19] .…”

Closely interleaved self-comparison method applied to precise measurement

“…As the most active field of time and frequency standards, atomic fountain clocks and optical clocks have shown great importance in the definition of the Système International (SI) second [1] , timing applications [2] , and numerous precise measurements [3,4] . Over several decades of development, 133 Cs and 87 Rb atomic fountain clocks have achieved a 1.1 × 10 −16 uncertainty [5] with a few parts in a 1 × 10 17 instability [2] .…”