Precision Inertial Measurements by Atom Interferometry – PIMAI

We will pursue instrumental developments on a state of the art cold atom gyrometer, located at the SYRTE laboratory. We will develop the concept of interlaced atomic interferometry, which allows to benefit from both high sensitivity and high bandwidth. A high bandwidth will represent a key improvement for instruments aiming to measure signals varying on time scales of one second, such as in inertial navigation. We will also study the hybridization of cold atom sensors with optical seismometers in order to reach the quantum noise limit in large area interferometers, traditionally limited by inertial noise. This research will lead to a cold atom gyroscope with a sensitivity and stability more than ten times higher than the best current fiber optic gyroscope.

We will study the improvement in performance offered by the use of an optical resonator to interrogate atoms. We aim to improve by an order of magnitude the scale factor of the interferometer with multi-photonic atomic separators realized in a resonant optical cavity for a centimeter-sized beam. This research will identify possible new designs for cold atomic sensors occupying a reduced volume and operating at higher sampling frequencies, two key points for field applications of quantum sensors.

We set up a new 2-dimensional magneto-optical trap that gives us a flux of atoms 3 times higher than the previous flux. We have imagined an alternative atom detection technique that reduces the complexity constraints associated with the atomic source to achieve a high measurement rate for interlaced atomic interferometry.

In January-February 2020, we set up a second axis for measuring rotation speeds, which is now operational. We have also reworked on the phase noise of Raman lasers, which is now 3 mrad per shot compared to 30 mrad previously, placing us close to the quantum projection noise.

We have implemented and demonstrated 2 important techniques for the cold atom gyroscope: a technique allowing to align the trajectories of atoms in order to constrain the bias to the level of 0.1 nrad/s (publication in Phys Rev A in 2019); another allowing to free ourselves from parasitic interferometers while eliminating the sensitivity to the accelerations of the instrument (publication in Phys Rev Letters in 2020).

We have finalized the study of the initially planned degenerated optical cavity. We were able to demonstrate an optical gain of 26 for a 2.8 mm diameter beam. Obtaining larger beams proved to be difficult and we have developed a numerical model to explain the behaviors observed when the beam size increases (publication in Optics Express in 2020).

- test of the Sagnac effect with matter waves with a relative accuracy of 50 ppm ;
- application of atomic gyrometry in seismology;
- implementation of the atomic interferometry techniques developed in this project in prototype gravitational wave detectors.

1. Degenerate optical resonator for the enhancement of large laser beams
Nicolas Mielec, Ranjita Sapam, Constance Poulain, Arnaud Landragin, Andrea Bertoldi, Philippe Bouyer, Benjamin Canuel, Remi Geiger
Optics Express Vol. 28, Issue 26, pp. 39112-39127 (2020)
arxiv.org/abs/2009.00941
2. Tailoring multi-loop atom interferometers with adjustable momentum transfer
L. A. Sidorenkov, R. Gautier, M. Altorio, R. Geiger, A. Landragin
Phys. Rev. Lett. 125, 213201 (2020)
arxiv.org/abs/2006.08371
3. Accurate trajectory alignment in cold-atom interferometers with separated laser beams
M. Altorio, L. A. Sidorenkov, R. Gautier, D. Savoie, A. Landragin, R. Geiger
Phys. Rev. A, 101, 033606 (2020)
arxiv.org/abs/1912.04793

11 presentations in international conferences.

After more than 25 years of research, cold-atom inertial sensors based on atom interferometry have reached sensitivity and accuracy levels competing with or beating inertial sensors based on different technologies. These sensors have several applications in geophysics, inertial sensing, metrology and fundamental physics. Enlarging their range of applications requires to constantly push further their performances in terms of sensitivity, stability, accuracy, dynamic range, compactness or robustness, ease-of-use, and cost.

More than 20 research groups and 4 companies worldwide are actively developing cold-atom inertial sensors for different applications, and investigating techniques to improve their performances. Regarding sensitivity improvements, the mostly studied methods involve large momentum transfer beam splitters for matter waves, long interrogation times, operations with ultra-cold atomic sources, and advanced detection or preparation methods. Other teams address specifically the concerns of simplifying the architecture of such sensors, pushing their dynamic range and/or sampling frequency for field applications, and improving their robustness. The objective of this ANR project is to pursue this research effort by studying new and generic atom interferometry techniques providing performance improvements, to characterize these techniques in a state-of-the-art instrument, and to use this instrument for precision inertial measurements.

The project will proceed along 3 lines of research. First, we will pursue generic instrumental developments on a state-of-the-art cold-atom gyroscope-accelerometer located at the SYRTE laboratory. We will develop the concept of interleaved atom interferometry, which allows to benefit from both high sensitivity and high bandwidth. High bandwidth will represent a key improvement for instruments aiming at measuring signals varying on second time-scales or faster, such as in inertial navigation or gravitational wave detection. We will also study the hybridization of cold-atom sensors with optical seismometers in order to reach the quantum projection noise limit in large-area atom interferometers, which are traditionally limited by inertial noise sources. These investigations will lead to a cold-atom gyroscope with a sensitivity and a stability more than ten times better than that of current best fiber-optics gyroscopes.

Second, we will use the cold-atom sensor for a test of fundamental physics. We will put at test the models of gravitational decoherence, which predict that macroscopic quantum superpositions decohere in the presence of the gravitational field generated by a local source mass.

Third, we will study the performance improvement offered by using an optical resonator to interrogate the atoms. We aim at improving by one order of magnitude the interferometer scale factor with large momentum transfer beam splitters performed in a large mode, top-hat, optical resonator. These investigations will determine possible new designs for cold-atom sensors occupying a reduced volume and operating at higher sampling frequencies, two key points for field applications of quantum sensors.

This project will require a multi-disciplinary approach involving expertise in metrology and instrumentation, atomic physics, precision optics, signal processing, geophysical modelling and gravitational physics.

In a highly competitive landscape, this project will allow a young researcher to foster key developments in atom interferometry and thereby to strengthen the position of France and Europe in this rapidly evolving field of quantum sensors and metrology. Besides the expected impact in atomic physics, geophysics, fundamental physics and inertial guidance, the know-how acquired in this project will impact the industrial development of cold-atom inertial sensors in France, in competitive sector where the SYRTE team can establish as a leader.