Quantum Absolute Sensors for Gravity Measurements

Gravity measurements are performed with two different classes of instruments: gravimeters, most widely used, measure the gravity acceleration gand its variations, whereas gradiometers measure its gradient.

Quantum gravity sensors, based on cold atom interferometry techniques, can offer higher sensitivities and accuracies than current state of the art commercial available technologies. Their limits in performances, both in terms of accuracy and long term stability, are linked to the temperature of the atomic cloud, in the low µK range, and more specifically, to the residual ballistic expansion of the atomic sources in the laser beams. To overcome these limits, we use ultracold atoms in the nano-kelvin range in our sensors.

I will first present our Cold Atom Gravimeter (CAG) used for the determination of the Planck constant with the LNE Kibble Balance [1]. It performs continuously 3 gravity measurements per second with a demonstrated long term stability of 0.06 nano-gin 40 000 s of measurement. Using ultracold atoms produced by evaporative cooling in a crossed dipole trap as a source, its accuracy, which is still to be improved, is currently at the level of 2 nano-g. This makes our CAG, the more accurate gravimeter [2]. It detects water table level variations. Then I will describe a « dual sensor » which performs simultaneous measurements of g and its gradient. This offers in principle the possibility to resolve, by combining these two signals, the ambiguities in the determination of the positions and masses of the sources, offering new perspectives for applications. It uses cold atom sources for proof of principle demonstrations [3, 4] and will soon combine ultra-cold atomic samples produced by magnetic traps on a chip and large momentum beamsplitters. With these two key elements, the gradiometer will perform measurements in the sub-E sensitivity range in 1 s measurement time on the ground. Such a level of performances opens new prospects for on field and on board gravity mapping, for drift correction of inertial measurement units in navigation, for geophysics and for fundamental physics.

 References

[1] M. Thomas et al. Metrologia 54, 468-480 (2017)

[2] R. Karcher, et al. New J. Phys. 20, 113041 (2018)

[3] M. Langlois et al. Phys. Rev. A 96, 053624 (2017)

[4] R. Caldani et al. Phys. Rev. A 99, 033601 (2019)