We perform Ramsey spectroscopy on the ground state of untracold 87Rb atoms magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities over the sample should reduce the contrast of the Ramsey frindges by a factor of 5 for 5 s of interrogation. We measure hardly any decay, only a factor 1.08 corresponding to a coherence time of the order of one minute. This new effect allows us to increase the quality factor of the microwave atomic resonance. We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect. The study of decoherence under metrological condition is the key to this synchronisation regime where non-linear effects dominate the evolution of the cloud. We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations. The effect is general and may appear in other physical systems with trapped atoms. In particular, this effect will exist for fermions and could be exploited to enhance the stability of optical lattice clocks.

The “watt balance” project aims at linking the kilogram definition to the Planck constant. The weighing of the mass involved requires a determination of the acceleration g with an uncertainty better than 10^-8. This work aims at determining g with an atomic gravimeter and a dedicated gravimetric site.

CNES, LKB and SYRTE are developing a primary frequency standard, called PHARAO, which is specially designed for space applications. The clock signal is referenced on the frequency measurement of the hyperfine transition performed on a cloud of cold cesium atoms (~1 µK). The transition is induced by an external field feeding a Ramsey cavity. In microgravity the interaction time inside the cavity can be adjusted over two orders of magnitude by changing the atomic velocity (5 cm·s^-1–5 m·s^-1) in order to study the ultimate performances of the clock. An engineering model has been assembled to validate the architecture of the clock. This model has been fully tested on ground for operation faults. Of course the clock performances are reduced by the effect of the gravity on the moving atoms. The main results are a frequency stability of 3.3 × 10^-13t^-1/2. The main systematic effects have been analyzed and their frequency uncertainties contribution is 1.6 × 10^-15. The clock has been compared with the primary frequency standard, the mobile fountain of SYRTE. The mean frequency shift is lower than 2 × 10^-15. The mechanical and thermal space qualifications have been carried out by testing a representative mechanical model of the clock and by using refined calculations. The design of the clock has been improved and now the flight model is being assembled. The PHARAO clock is a key instrument of the European ESA space mission called ACES. This mission is dedicated to perform space-time measurements in order to test some fundamental physics aspects.

The distribution and the comparison of an ultrastable reference frequency using optical fibres have been greatly improved in the last ten years. LNE-SYRTE and LPL (University Paris 13) have been pioneering the development of these new methods. In this paper we present a review of the methods and the results obtained. The frequency stability and accuracy of optical links surpass the well-established methods using GNSS and geostationary satellites. In this paper we show that it is possible to use public telecommunication network carrying Internet data to compare and distribute ultrastable metrological signals over long distances. In addition both frequency stability and accuracy are equivalent to those obtained with links developed with a dedicated fibre network. This novel technique paves the way to the deployment of a national and continental wide ultrastable metrological optical network.

The kilogram is the last unit of the International System of Units (SI) still defined by an artefact, namely the International Prototype of the Kilogram (IPK). Comparisons carried out over 100 years between IPK, its official copies and national prototypes have revealed a mass change (in relative term) of five parts in 108. After a brief history of the unit of mass, this paper underlines the need to redefine the kilogram with reference to a fixed numerical value of a fundamental constant. It explains why the Planck constant h was chosen and gives the last results obtained with watt balance experiments nowadays able to link h to a macroscopic mass to within a few parts in 108. Finally, it proposes a possible route for the national metrology institute for the mise en pratique of the kilogram after its redefinition.

In optical lattice clocks, an ensemble of cold neutral atoms confined in a lattice-shaped dipole trap are probed by an ultrastable laser. They have recently become the best frequency references, because they combine a narrow atomic resonance in the optical domain – hence a large quality factor – and a large number of simultaneously probed atoms. In this paper, we present the latest developments of these clocks, both in terms of frequency stability and accuracy, by focusing on two strontium optical lattice clocks under operation at LNE-SYRTE.

We present the new cold atom gyroscope experiment developed at SYRTE since 2009. The experiment is based on a fountain configuration and a four light pulse atom interferometer which allows to reach a Sagnac area of at least 11 cm². We demonstrated a gyroscope stability of 3 nrad·s⁻¹ after 1 000 s of integration, which represents the state of the art for cold atom gyroscopes. Here we describe the main elements of the setup and the near future evolutions of the experiment to achieve better sensitivity levels.