When an atom propagates through a dilute medium, the wave that describes its propagation is modified by the interaction with the medium. In the present paper, we propose to treat this modification by introducing an index of refraction. This is a natural extension of this idea so familiar for light propagation, and such an extension has already been made in the case of neutrons in dense matter. Various interesting consequences of this idea are explored, most particularly in the case of ultracold atoms as the refraction index diverges in the quantum threshold limit.

• Received 21 July 1994

DOI:https://doi.org/10.1103/PhysRevA.52.3973