It is shown that the deflection of an atom de Broglie wave at a nonres
onant weak cavity field mode can yield a pure entangled quantum state
in which discernable atomic beams ate entangled to photon number state
s of the field and to internal states of the atom. The proposed experi
mental scheme is shown to be applicable for quantum nondemolition meas
urement of the photon statistics, and for quantum state engineering an
d reconstruction experiments.