  There should be quantum vacuum fluctuations of spacetime itself, if we accept
that the basic quantum principles we are already familiar with apply as well to
a quantum theory of gravity. In this paper, we study, in linearized quantum
gravity, the quantum entanglement generation at the neighborhood of the initial
time between two independent gravitationally polarizable two-level subsystems
caused by fluctuating quantum vacuum gravitational fields in the framework of
open quantum systems. A bath of fluctuating quantum vacuum gravitational fields
serves as an environment that provides indirect interactions between the two
gravitationally polarizable subsystems, which may lead to entanglement
generation. We find that the entanglement generation is crucially dependent on
the polarizations, i.e, they cannot get entangled in certain circumstances when
the polarizations of the subsystems are different while they always can when
the polarizations are the same. We also show that the presence of a boundary
may render parallel aligned subsystems entangled which are otherwise
unentangled in a free space. However, the presence of the boundary does not
help in terms of entanglement generation if the two subsystems are vertically
aligned.
