  We investigate the effect of entanglement dynamics due to gravity -- the
basis of a mechanism of universal decoherence -- for photonic states and
quantum memories in Mach-Zehnder and Hong-Ou-Mandel interferometry setups in
the gravitational field of the earth. We show that chances are good to witness
the effect with near-future technology in Hong-Ou-Mandel interferometry. This
would represent an experimental test of theoretical modeling combining a
multi-particle effect predicted by the quantum theory of light and an effect
predicted by general relativity. Our article represents the first analysis of
relativistic gravitational effects on space-based quantum memories which are
expected to be an important ingredient for global quantum communication
networks.
