  Diffraction of matter-waves is an important demonstration of the fact that
objects in nature possess a mixture of particle-like and wave-like properties.
Unlike in the case of light diffraction, matter-waves are subject to a
vacuum-mediated interaction with diffraction obstacles. Here we present a
detailed account of this effect through the calculation of the attractive
Casimir-Polder potential between a dielectric sphere and an atomic beam.
Furthermore, we use our calculated potential to make predictions about the
diffraction patterns to be observed in an ongoing experiment where a beam of
indium atoms is diffracted around a silicon dioxide sphere. The result is an
amplification of the on-axis bright feature which is the matter-wave analogue
of the well-known `Poisson spot' from optics. Our treatment confirms that the
diffraction patterns resulting from our complete account of the sphere
Casimir-Polder potential are indistinguishable from those found via a
large-sphere non-retarded approximation in the discussed experiments,
establishing the latter as an adequate model.
