6 May 2019
Contributions to international timescales
The first application of atomic fountain is to realize the second of the international system of units. It is the BIPM (International Bureau for Weights and Measures) which is in charge of centralizing the data of the contributing laboratories and of calculating the international timescales: UTC (Coordinated Universal Time) and TAI (International Atomic Time), as well as the second of the SI. Currently, over the twenty or so atomic fountains under development or operating in various countries, about half a dozen regularly contribute to TAI/UTC/SI, among which the three SYRTE fountains. Thanks to a quasi uninterrupted operation of its fountains, the SYRTE contribution represents about 40% of the international contributions to the steering of the international timescales since about ten years. Note also that since 2013, FO2-Rb, just as the cesium fountains, contributes to the steering of the TAI as a secondary representation of the second, following a process to implement new procedures performed in tight collaboration with the BIPM. This work realized with FO2-Rb prefigures the exploitation of optical clocks which will probably be the basis to a future redefinition of the SI second.
Generation of the legal time
Thanks to their almost continuous operation, the SYRTE fountains provide frequency calibrations of our reference hydrogen maser on a dayly basis, from which the reference time UTC(OP), Coordinated Universal Time of Observatoire de Paris, is generated. UTC(OP) is the national real time realization of UTC and constitutes the legal time broadcasted in France. Thanks to the accuracy of SYRTE fountains UTC(OP) has become one of the three best representations of UTC in the world.
Other applications
Cold atom fountains also constitute highly accurate measuring instruments regarding applications in time-frequency metrology (tests of time transfer techniques T2L2, GPS, TWSTFT, optical fiber links), in atomic physics (observation of Feshbach resonances, …), in fundamental physics (tests of Lorentz invariance, tests of the stability of the fundamental constants such as for example the fine structure constant).
As primary frequency standards, cesium fountains regularly serve in absolute frequency measurement campaigns of clocks based on other atomic species, in particular the SYRTE optical lattice clocks.
Atomic fountains, just as optical clocks and oscillators and SYRTE time references, will be key elements of the ground segment of the space mission ACES/PHARAO, for which the SYRTE play a major role since twenty years or so.
- The atomic fountains, part of the SYRTE clock ensemble