  We review recent theoretical results, obtained for the equivalence between
gravitational mass and energy of a composite quantum body as well as for its
breakdown at macroscopic and microscopic levels. In particular, we discuss that
the expectation values of passive and active gravitational masses operators are
equivalent to the expectation value of energy for electron stationary quantum
states in a hydrogen atom. On the other hand, for superpositions of the
stationary quantum states, inequivalence between the gravitational masses and
energy appears at a macroscopic level. It reveals itself as time-dependent
oscillations of the expectation values of passive and active gravitational
masses, which can be, in principle, experimentally measured. Inequivalence
between passive gravitational mass and energy at a microscopic level can be
experimentally observed as unusual electromagnetic radiation, emitted by a
macroscopic ensemble of the atoms. We propose the corresponding experiment,
which can be done on the Earth's orbit, using small spacecraft. If such
experiment is done it would be the first direct observation of quantum effects
in general relativity.
