We show that the accuracy of atomic interferometry can be improved by
using QND measurements of the atomic populations at the inputs to the
interferometer. The accuracy of such a scheme surpasses the standard q
uantum limit of phase measurement delta phi(SQL) = 1/root N and could
reach the Heisenberg limit delta phi similar to 1/N. We propose to per
form QND measurements of atomic populations with an off-resonant laser
field. The conditions necessary for this kind of QND measurement coul
d be fulfilled in a variety of ways with current experimental techniqu
es, including magneto-optical traps and atomic cells.