Franck Pereira dos Santos
Observatoire de Paris
Franck Pereira Dos Santos is a Researcher with the National Centre for Scientific Research (CNRS). He graduated from the Ecole Normale Supérieure in Paris and received the Ph.D. degree in physics from the Université Pierre et Marie Curie in 2002. Since 2002, he has been with the Laboratoire National de Métrologie et d’Essais–Systèmes de Référence Temps Espace (LNE-SYRTE), at Paris Observatory. He is heading the “Atom Interferometry and Inertial Sensors” team, a leader in the development of cold atom inertial sensors. His research focuses on the realization and study of gravity sensors based on free fall and trapped atom interferometry.
Cold atom gravimeters constitute today one of the most mature inertial sensors based on atom interferometry. They reach performances better than their classical counterparts, both in terms of short term sensitivity and long term stability, and in contrast with the latter, offer the possibility to perform high repetition rate continuous measurements over extended periods of time. These features have motivated the development of commercial sensors, addressing in particular applications in the fields of geophysics.
Best accuracies in the 30-40 nm/s2 range have been reported for these instruments and validated through the participation of these instruments to international comparisons of absolute gravimeters. The limit in their accuracy is linked to the wavefront distortions of the lasers beamsplitting pulses, arising from reflection and transmission through imperfectly flat optics, which lead to parasitic phase shifts sampled by the atoms at the interferometer pulses and to a bias in the gravity measurement. This bias depends on the expansion of the atomic source across the interferometer laser beams, and thus on the atomic temperature. Extrapolating the measurements to zero temperature allows in principle to correct for this effect.
To tackle this problem and reduce the uncertainty on the evaluation of this effect, we have implemented ultracold atoms, produced by evaporative cooling in a high power dipole trap, as a source in our high accuracy atom gravimeter. Gravity measurements have then been performed with state of the art statistical uncertainties in a so-far largely unexplored temperature range for such a high accuracy sensor, down to about 50 nK. A thorough model of the impact of optical aberrations onto the instrument has been developed and a method proposed to correct for this effect. A gain of a factor 3 in the accuracy is demonstrated with a first set of measurements [1], which will be improved further by performing more measurements, especially at lower temperatures. This result demonstrates the benefit the use of ultracold atoms can bring to the metrology of atom interferometry inertial sensors.
[1] R. Karcher, A. Imanaliev, S. Merlet, F. Pereira dos Santos, "Improving the accuracy of atom interferometers with ultracold sources", arXiv:1804.04909
