Lithium atom interferometry

We have built an atom interferometer of the Mach Zehnder type. The atomic wave ($\lambda_{\it dB}=54$ pm) is a supersonic beam of lithium seeded in argon. The realization of mirrors and beams splitters for the atomic wave relies on elastic Bragg diffraction on laser standing waves at $\lambda= 671$ nm. We first present our experimental setup and signals with atomic fringes which exhibit a very high visibility, up to $84.5 \pm 1 \%$, and a very large phase sensitivity. This phase sensitivity is then used to perform an absolute measurement of the lithium atom electric polarizability by applying an electric field on only one atomic beam in the interferometer. Our result, $\alpha= (24.33 \pm 0.16) \times 10^{-30}$ m$^3$, reduces by a factor three the uncertainty of the best previous measurement