  The Schr\"odinger equation for an atomic beam predicts that it must have a
phase anomaly near the beam waist analogous to the Gouy phase of an
electromagnetic beam. We propose here a feasible experiment which allows for
the direct determination of this anomalous phase using Ramsey interferometry
with Rydberg atoms. Possible experimental limitations are discussed and shown
to be completely under control within the present day technology. We also
discuss how this finding can open the possibility to use the spatial mode
wavefunctions of atoms as q-dits, since the Gouy phase is an essential
ingredient for making rotations in the quantum states.
