``Interaction-free'' interaction: Entangling evolution coming from the possibility of detection

The dynamical version of the so-called ``interaction-free'' measurement [Phys. Rev. Lett. 74 (1995) 4763] is presented, in which the object called ``bomb'' is replaced with the atom evolving coherently. It is pointed out that, due to the quantum Zeno effect, the ``explosion'' symbolized by the absorption of a photon by the atom will never take place. It is shown, however, that this is accompanied by a strong modification of the involved evolution which now has a highly entangling character. Properties of the new evolution are discussed. It is also proved that beyond the quantum Zeno effect regime there is a natural possibility of conditional (i.e., followed by the sequence of some, but not necessarily frequent, probes) freezing of the evolving system in a maximally entangled state. An explanation of the effects as well as some general conclusions are provided.