  The differential cross section for gravitational photon-photon scattering
calculated in Perturbative Quantum Gravity is shown to depend on the degree of
polarization entanglement of the two photons. The interaction between photons
in the symmetric Bell state is stronger than between not entangled photons. In
contrast, the interaction between photons in the anti-symmetric Bell state is
weaker than between not entangled photons. The results are interpreted in terms
of quantum interference, and it is shown how they fit into the idea of
distance-dependent forces.
