Implementation of an ultra-cold atom source to improve the accuracy of an atomic gravimeter

This thesis aims to improve the accuracy of the Cold Atom Gravimeter from LNESYRTE. This gravimeter employs atom interferometry techniques to measure the local gravity acceleration g of free falling Rubidium 87 cold atoms. This gravimeter is the national metrological reference meaning that all its biases must be evaluated with the best accuracies. At the beginning of this thesis, the total accuracy budget of 4.3 µGal, was dominated by the uncertainty on the wavefront aberration bias which accounted for 4.0 µGal. In order to improve the evaluation of this effect, we implemented an ultra-cold atom source. With this source, we performed g measurements over a wide range of temperatures. The developpment of a complete model of the experiment and a siimulation of the impact of the wavefronts on the g measurements allowed us to gain insights on the evaluation of this bias which uncertainty was thus improved by a factor three and is now 1.3 µGal. Finally, the gravimeter participated in the Kibble balance project which goal was to link the Planck constant to the kg unit. This project needed the determination and transfer of the absolute g value. We contributed to the revolution of the International System of Units: the Planck constant is now fixed and the definition of the kg is modified. This new definition is now effective since the 20 May 2019.

gravimetry, fundamental metrology, inertial sensor, atom interferometry, Raman transitions, ultra-cold atoms, dipole trap, Kibble balance, kilogramme redefinition

Full document: https://tel.archives-ouvertes.fr/tel-02950853