  Entangled photon pairs-discrete light quanta that exhibit non-classical
correlations-play a central role in quantum information and quantum
communication technologies. It is a natural demand from technological
applications on the intensity of the entangled photon pairs, such that
sufficient signal strength can be achieved. Here we propose approaches based on
klystron tubes that could potentially achieve stable amplification of the
entangled photon pairs generated by spontaneous parametric down conversion
(SPDC) and entanglement transfer.
