  In order to show that the graviton is a quantum entity an experiment is
proposed that can show that quantum entanglement is produced by means of an
exchange of gravitons. For this to be possible, one has to be able to witness
the entanglement between the two objects considered in the experiment and to be
able to eliminate other sources of entanglement like the exchange of virtual
photons. Graviton mediated polarisation-polarisation photon entanglement is
being analysed by methods originating from the Schwinger Keldysh and the
Kadanoff Baym formalisms in conjunction with quantum Boltzmann type equations.
Applications in the context of cosmology are discussed.
