Realisation of an atomic gradiometer based on Bragg diffraction

This manuscript details the thesis work done at SYRTE on the cold atom gradiometer experiment. The gradiometer is a quantum sensor using two cold atom interferometers to measure the gravity acceleration at two distinct locations in space and thus measure locally the gravity gradient. The sensor was functional at the beginning of this work, with two cold atom sources and an interferometer using Raman pulses. In order to improve the sensitivity of the instrument, the researcher has implemented and characterized diffraction of the atoms in the quasi-Bragg regime and they have realized interferometers for different diffraction orders. The output ports being in the same internal state but on two different momentum states, it is difficult to measure them independently with a classical time-of-flight detection method. A new method has been therefore developed and characterized to increase their spatial separation before detection using a Bloch elevator. The team also implemented a Bloch elevator at the beginning of the sequence in order to operate the interferometer in a fountain configuration and take advantage of a maximum free fall time. A mirror mounted on a tip tilt have been characterized to compensate for the Coriolis acceleration experienced by the atoms during their fall and a flat top collimator was implemented on the experiment to illuminate the atoms in a uniform way. A sensitivity to the gravity gradient of 213 E at one second (1 E = 10^‒9 s^‒2) has been demonstrated.

atomic interferometry, cold atoms, gravimeter, gradiometer, metrology

Full document (FR) : TEL-03990195