Measurement of the electric polarizability of lithium by atom interferometry

We have built an atom interferometer and, by applying an electric field on one of the two interfering beams, we have measured the static electric polarizability of lithium {alpha}=(24.33{+-}0.16)x10{sup -30} m{sup 3} with a 0.66% uncertainty. Our experiment is similar to an experiment done on sodium in 1995 by Pritchard and co-workers, with several improvements: the electric field can be calculated analytically and the interference signals have a large intensity and a high visibility, resulting in accurate phase measurements. This experiment illustrates the extreme sensitivity of atom interferometry: when the atom enters the electric field, its velocity increases and the fractional change, equal to 4x10{sup -9} for our largest field, is measured with a 10{sup -3} accuracy.