  It is discussed how systems of quantum-correlated (entangled)particles or
atoms behave in external gravitational fields and what gravitational effects
may exist in such systems. An experimental setup is proposed which improves the
sensitivity of the Ramsey interferometer by the usage of quantum-correlated
atoms. Entanglement of $n$ atoms improves the sensitivity to small phase shifts
in $n^2$ times. This scheme may be used for observing gravity-induced phase
shifts in laboratory.
