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Quantum tests of the Equivalence Principle with Atom Interferometry

The weak Equivalence Principle (EP) represents a corner stone in the General Theory of relativity. The validity of this postulate was and is currently tested in different groups with different systems. Among this multitude atom interferometry is considered to be one of the most powerful tools in performing high-precision measurements. In a typical experiment testing the EP with interferometric measurements, the cold atoms (µK regime or colder) are experiencing a gravitational field leading to a phase shift between the two arms of the interferometer. This shift is proportional to the gravitational acceleration and can be measured accurately using cold atom beams splitted and recombined by laser pulses. Using two atom species with sensibly different masses will allow us to compare two independent measurements of g. This is made possible by creating simultaneously in a single experiment a mixture of two atomic species at a temperature close to the absolute zero. This regime is suitable to the observation of matter waves at long time scales needed for quantum tests. An overview of the last developments of these quantum sensors in our group will be presented during the talk. In fact two experiments are developed aiming to the realization of mixtures of Bose-Einstein Condensates (BECs) of Rubidium and Potassium to be used as coherent sources of atom interferometers. The first experiment (ATLAS) has the goal to create BECs by all-optical means i.e. by loading a cloud of magneto-optically cooled atoms in a laser dipole guide. An evaporation stage follows in order to achieve the quantum degeneracy. Coupled to a set of Raman lasers this device is a multi-species and compact atom interferometer. The second experiment (the Quantus Project) aims to overcome Earth-bound laboratory restrictions (such as the need for levitation and mass dependant confining potentials) by operating in microgravity environments. A first step was already accomplished by realizing a complete BEC experiment in free fall giving birth to a giant and coherent matter wave of several millimeters expanding freely during one second. The second generation of this project deals with the conception of a source of 87Rb and 40K as degenerate Bose and Fermi gases respectively to be used to carry out inteferometry experiments operated in a catapult mode offering microgravity times of 9 seconds. Up to date progress and future prospects of these ambitious and technically challenging projects will be presented in the conference.

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