  A direct consequence of quantization of gravity would be quantum
gravitational vacuum fluctuations which induce quadrupole moments in
gravitationally polarizable atoms. In this paper, we study the spontaneous
excitation of a gravitationally polarizable atom with a uniform acceleration
$a$ in interaction with a bath of fluctuating quantum gravitational fields in
vacuum, and compare the result with that of a static one in a thermal bath of
gravitons at the Unruh temperature. We find that, under the fluctuations of
spacetime itself, transitions to higher-lying excited states from the ground
state are possible for both the uniformly accelerated atom in vacuum and the
static one in a thermal bath. The appearance of terms in the transition rates
proportional to $a^4$ and $a^2$ indicates that the equivalence between uniform
acceleration and thermal field is lost.
