Index of refraction of noble gases for sodium matter waves

We present a theoretical study of the index of refraction of the light noble gases He and Ne for the propagation of sodium matter waves. Our approach is based on the well known multiple scattering theory inside a medium, which leads to an approximation for the index of refraction that depends only on the single forward scattering amplitude and the density distribution functions for the atoms of the medium. The forward scattering amplitude between a sodium atom and a noble gas atom is calculated from molecular potential curves using the eikonal approximation. An explicit phase space average is performed over the noble gas atom distribution in the medium. Our results show very good agreement with the recent interferometry measurements of Schmiedmayer er al. [Phys. Rev. Lett. 74, 1043 (1995)]. Our calculations provide an interpretation of the experimental data, and may shed some light on possibilities for obtaining improved interatomic potentials through atomic interferometry measurements.