Two-dimensional motion of cold atoms in a near-resonant annular laser beam: Artificial two-dimensional molecules

We develop the theory of the two-dimensional motion of cold atoms in a near-resonant annular laser beam. For a red-detuned field the laser beam provides an annular light shift potential and the atomic motion divides into vibrational and rotational normal motions analogous to a two-dimensional molecule. In the ground vibrational state we obtain an atom optics realization of a two-dimensional rotator. We illustrate the novel physics which may be explored with this system by showing that gravity acts analogously to a static electric field applied to a charged rotator.