  The wave function of an atom passed through a diffraction grating acquires a
regular space structure and the interaction of another particle with this atom
can be thought of as scattering on a 'quantum grating' composed of a single
atom. Probing this 'grating' by collisions with charged projectiles reveals
interference effects due to coherent contributions of its 'slits' to the
transition amplitude. In particular, the spectra of electrons emitted from the
atom in collisions with swift ions exhibit a pronounced interference pattern
whose shape can be extremely sensitive to the collision velocity.
