  It is found that the differential cross section of photon-photon scattering
is a function of the degree of polarization entanglement of the two-photon
state. A reduced, general expression for the differential cross section of
photon-photon scattering is derived by applying simple symmetry arguments. An
explicit expression is obtained for the example of photon-photon scattering due
to virtual electron-positron pairs in Quantum Electrodynamics. It is shown how
the effect in this explicit example can be explained as an effect of quantum
interference and that it fits with the idea of distance-dependent forces.
