ECAMP 15

Using wave properties of matter, cold atoms can become tiny quantum sensors with high stability and sensitivity to inertial quantities, such as rotation or acceleration. The principle of a cold-atom gravimeter is the following: cold atoms (a few μK) free fall in an ultra-high vacuum chamber, submitted to the Earth gravity g. While they are falling, one can probe the atoms with lasers in a matter-wave Mach-Zehnder interferometer: carefully-tuned laser pulses will transfer momentum to the atoms which will result in the matter wave being separated, deflected and recombined. At the end of the interferometer one can get the value of g by measuring the phase of the atoms via fluorescence.
Contrary to their classical counterparts, cold-atom accelerometers suffer from dead times between each measurement (corresponding to the laser cooling sequence) and have a limited measurement range. However, they do benefit from an unrivalled stability and allow to perform absolute measurements [1]. Since classical and atomic sensors have complementary strengths and weaknesses, they are both commonly combined to create hybrid sensors. Unfortunately, hybrid sensors could be limited by the intrinsic noise of the classical sensor. However, there could be another way to make the best of the atomic accelerometer: manipulating different atomic species simultaneously inside the same sensor.
Indeed, there are insightful configurations using 3 atomic species (${}^{85}$Rb, ${}^{87}$Rb and ${}^{133}$Cs) instead of one. One could decrease dead times by” juggling” between the 3 species such that while one species is being laser-cooled, the other is free-falling in the matter-wave Mach-Zehnder and the third species is being detected. Another configuration could enable simultaneous 3D acceleration measurements. The challenge is to imagine and set up ingenious configurations to exploit the full potential of the triple species gravimeter, dealing with interspecies interactions while keeping the set-up compact and robust for possible applications in dynamic environment. In this regard, we have developed an all-fibered laser system based on telecom laser diodes at 1.5 µm and at 1.9 µm.
A first triple species magneto-optical trap has been obtained and its characteristics such as the loading time or the number of atoms are to be studied, as they contain information on the collision processes. Meanwhile, a numerical simulation is developed to investigate the impact of deadtimes in the context of on-board measurements, as well as highlight the benefits of a triple-species continuous measurement.

[1] Bidel, Y. et al., Absolute marine gravimetry with matter-wave interferometry. Nature Commun, https://doi.org/10.1038/s41467-018-03040-2