Laboratoire Collisions Agrégats Réactivité - UMR5589

Using an atom interferometer, we have measured the static electric polarizability of ⁷Li
α=(24.33 ±0.16)×10^-30 m³
= 164.2±1.1 atomic units with a 0.66% uncertainty. Our
experiment,
which is similar to an experiment done on sodium in 1995 by Pritchard
and co-workers, consists in applying an electric field on one of the
two interfering beams and measuring the resulting phase-shift. With
respect to Pritchard’s experiment, we have made several improvements
which are described in detail in this paper: the capacitor design is
such that the electric field can be calculated analytically; the phase
sensitivity of our interferometer is substantially better, near
16 mrad/√Hz finally our interferometer is species selective so that impurities
present in our atomic beam (other alkali atoms or lithium dimers) do
not perturb our measurement. The extreme sensitivity of atom
interferometry is well illustrated by our experiment: our measurement
amounts to measuring a slight increase Δv of the atom velocity v when
it enters the electric field region and our present sensitivity is
sufficient to detect a variation Δv/v ≈6 ×10^-13.