Reference : UMR8630-SEBMER-002
Workplace : PARIS 14
Date of publication : Thursday, June 16, 2022
Scientific Responsible name : Sébastien Merlet
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 3 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Our team develops inertial sensors (accelerometers, gyrometers, …) based on atom interferometry technics. The development of this technology is linked to the use of cold atoms and laser beamsplitters, namely two photon transitions and more specifically stimulated Raman transitions. These methods allow now for the development of commercial products with applications in geophysics on the field.
We have developed a state-of-the-art cold atom gravimeter (CAG), based on these techniques. It uses free-falling 87Rb atoms, which experience a sequence of Raman pulses driven by counter-propagating vertical lasers. The atom interferometer phase shift is proportional to g, the Earth gravity acceleration that we measure with a sensitivity better than conventional state of the art absolute gravimeters
(5.7ng@1s)  and more accurately (2ng) .
Limits have been identified and several improvements will be made to reach the 10-10 range both in term of accuracy and stability.
The vacuum chamber will be modified to allow to use a new crossed dipole trap with a 50W laser at 1.1μm. We will take advantage of the reopening of the vacuum chamber to install a rotatable retroreflexion mirror for the Raman lasers. This will improve our control of the laser alignment and allow to compensate Coriolis acceleration. In order to improve our control on the initial position of the atoms,
new MOT collimators will be installed, as well as an innovative fiber splitter system for the control of the powers in each MOT beam.
The PhD will integrate the team and work on (i) the implementation and optimization of the optical trap, (ii) the characterization and optimization of the reflexion system and (iii) the control of the initial cloud position.
The ultimate aim is to improve the evaluation of Coriolis acceleration and wavefront distortions effects
even further, by performing measurements at very low temperature, and with more atoms. This will require to optimize the evaporation sequence, by increasing the capture volume of the trap using modulation techniques. Yet, a drawback when using dense samples of ultracold atoms, eventually Bose-Einstein condensed, instead of a more dilute laser cooled source, arises from the effect of interatomic
interactions, which we will investigate. The obtained uncertainty budget and sensitivity performances will finally be tested during comparisons with absolute and superconducting gravimeters .
The PhD will interact and work at SYRTE (i) with two permanent researchers, a PhD student already working on the gravimeter and a PostDoc that is to be hired and (ii) with h/m team at LKB. Indeed, the PhD project is a part of a collaborative project between SYRTE and LKB supported by ANR and the regional network SIRTEQ. In particular, tight interactions are foreseen with a joint PhD student between our two
teams, who will be in charge of modeling the instruments. This will help to consolidate the accuracy budget to be performed in the frame of this PhD project.
 P. Gillot, O. Francis, A. Landragin, F. Pereira dos Santos and S. Merlet, Stability comparison of two absolute gravimeters: optical versus atomic interferometers, Metrologia 51 (2014) L15-L17
 R. Karcher, A. Imanaliev, S. Merlet and F. Pereira dos Santos, Improving the accuracy of atom interferometers with ultracold atoms, New J. of Phys. 20 (2018) 113041
 S. Merlet, P. Gillot, B. Cheng, R. Karcher, A. Imanaliev, L. Timmen and F. Pereira dos Santos, Calibration of a superconducting gravimeter with an obsolute atom gravimeter, J. Geod 95, (2021) 62
The activity of the team Atom Interferometry and Inertial Sensors of SYRTE - Observatoire de Paris concerns the applications of atom interferometry to high precision measurements, and especially to the realization of inertial sensors. The principle of the duality between wave and matter postulates that to each particle a wave-packet (called de Broglie wave) can be associated, which can be manipulated in the same way as light in optics. For example, these atom wave-packets can be split or recombined to make them interfere. In an atom interferometer, the splitting between the two partial wave-packets associated to the same atom gives an extremely high sensitivity to inertial forces as acceleration and rotation. Our experiments use cold atom samples, cooled down thanks to lasers, which enable increasing drastically the measurement time and thus the sensitivity. One of the interest of atom interferometry arises from its ability to provide very stable and accurate measurements, which are required for use in various fields of application, such as inertial navigation, geophysics or fundamental physics.
Our team is a pioneer in the development of these sensors, and has acquired an expertise well recognized at the international level, in particular in the metrological study of these instruments. We have realized the demonstration of the first cold atom gyroscope, and have been the first team to participate to international comparisons of absolute gravimeters, with our cold atom gravimeter, and to demonstrate operation without dead times of this type of sensors. We have established records in performances both in terms of stability and accuracy in gyrometry, gravimetry and in frequency and force measurements with trapped atom sensors.
Our numerous contributions to the domain (models for the evaluation of the limits in the sensitivity and accuracy, development of technics for vibration noise rejection, demonstration of novel sensor architectures, development of hybridization technics ...) are today widely used by other teams active in the domain. Our work in gravimetry has been transfered to the Muquans company, who commercializes cold atom gravimeters based on our patented technology.
Constraints and risks
Use of lasers
We talk about it on Twitter!