Nowadays, the most accurate realization of the second, i.e. the unit of time, is provided by fountains of laser-cooled cesium atoms. All the atomic fountain clocks presently contributing to the International atomic time scale (Temps atomique international TAI) operate in pulsed mode: the atoms are successively laser-cooled to a few micro-kelvin, launched upward vertically, and their oscillation frequency is measured during the ballistic flight, before the cycle starts over again.

In our group, we explored an alternative approach by developing a continuous fountain of laser-cooled atoms in collaboration with the Swiss federal office of metrology METAS. This original approach to the definition of time is important since it provides the metrological biodiversity which is necessary to guarantee that the second is independent of the method used for its realization. The present research project aims at the accuracy evaluation of our continuous atomic fountain clock. It will put the continuous fountain approach, a unique Swiss specialty, at the forefront of fundamental metrology, by providing the potentially most stable and accurate cesium fountain clock worldwide.

Once in operation at METAS, this clock will contribute to improving the International atomic time scale TAI. It will reinstate Switzerland in the very limited number of countries contributing significantly to time and frequency metrology at its most fundamental level.