The aim of this new project is to study short range interactions using atom interferometry techniques. This experiment will allow realizing precise measurements of gravity at short distance, searching for possible deviations to Newtonian gravity. Such deviations are made possible by new gravitational-type interactions with range on the order of the micrometer, as considered by various unification theories. The measurement of such interactions appears as a promising way for the observation of the first experimental signals of new physics beyond the standard model.

The FORCA-G project will set constraints (or discover new physics) on the interactions at short distance, focusing its investigation in the micrometer range. A simple phenomenological model describes a potential new interaction as a modification of the Newtonian potential with a Yukawa type term :

where is the Newtonian potential, and α and λ are the amplitude and the range of the new interaction. The goal of the project is to improve the sensitivity on α for ranges from 100 nm to 10 μm, and a precise measurement (and cancellation) of the Casimir-Polder potential between an atom and a surface. This last effect, which constitutes the dominant limitation for the measurement of new interactions, deserves precise study in itself: it is the most accessible manifestation of quantum field fluctuations in the macroscopic world.

A more detailed description of the experiment is available on the web site of the Atom Interferometry and Inertial Sensors team. The principle is based on the initial proposal by P. Wolf et al, Phys Rev A 75, 063608 (2007) and consists of trapping Rb atoms in an optical lattice formed by a laser. The reflecting mirror acts as the surface with which the atoms interact.

The Theory and Metrology team has accompanied this experiment by detailed theoretical modelling and the estimation of teh expected uncertainty. A first result was the calculation of the atomic quantum states in the context of the experiment, and in particular close to the surface.

Atomic states close to the surface

Wave functions of the four states closest to the surface as a function of distance z (in units of = 266 nm). In red the corresponding states far from the surface.

Following that we have modelled and suggested different interferometric configurations using those states with the aim of optimising the performance for the measurement of the Casimir-Polder effect as well the serach for deviations from Newton’s law. We have estimated the performance based on the expected experimental noise and uncertainty.

Yukawa limits expected from FORCA-G

Expected limits from FORCA-G on Yukawa type interactions in the plane (see above) in red and dashed, with the present exclusion zone in yellow.

These results were published in:

Messina, R.; Pelisson, S.; Angonin, M.-C. & Wolf, P., Atomic states in optical traps near a planar surface Phys. Rev. A, 2011, 83, 052111.

Pelisson, S.; Messina, R.; Angonin, M.-C. & Wolf, P., Dynamical aspects of atom interferometry in an optical lattice in proximity to a surface Phys. Rev. A, 2012, 86, 013614.

Pelisson, S.; Messina, R.; Angonin, M.-C. & Wolf, P., Lifetimes of atoms trapped in an optical lattice in proximity of a surface Phys. Rev. A, 2013, 88, 013411.