The standard quantum limit is calculated for the atom-light interferom
eter. It is shown that the smallest detectable phase is delta phi(min)
= 1/2[N-atoms + 4N(photons))/NatomsNphotons](1/2). Therefore, in prac
tical experiments, the accuracy is limited by the square root of the n
umber of atoms. We propose a novel correlated atom-photon state interf
erometer which makes a transition to the Heisenberg limit, delta phi(m
in), proportional to 1/N-atoms, as the atoms approach a Bose condensat
e. Such an interferometer may serve as a sensitive probe of the onset
of Bose condensation. Finally, we point out that the correlated atom-p
hoton state preparation scheme we propose may be used in a different w
ay to approach the Heisenberg limit for non-Bose-condensed atoms.