  We report experimental results on mixed-state generation by multiple
scattering of polarization-entangled photon pairs created from parametric
down-conversion. By using a large variety of scattering optical systems we have
experimentally obtained entangled mixed states that lie upon and below the
Werner curve in the linear entropy-tangle plane. We have also introduced a
simple phenomenological model built on the analogy between classical
polarization optics and quantum maps. Theoretical predictions from such model
are in full agreement with our experimental findings.
