  The emission of entangled light from planar semiconductor microcavities is
studied and the entanglement properties are analyzed and quantified.
Phase-matching of the intra-cavity scattering dynamics for multiple pump beams
or pulses, together with the coupling to external radiation, leads to the
emission of a manifold of entangled photon pairs. A decomposition of the
emitted photons into two parties leads to a strong entanglement of the
resulting bipartite system. For the quantification of the entanglement, the
Schmidt number of the system is determined by the construction of Schmidt
number witnesses. It is analyzed to which extend the resources of the
originally strongly entangled light field are diminished by dephasing in
propagation channels.
