"Interaction-free" interaction: Entangling evolution coming from the possibility of detection - art. no. 022108

The dynamical version of the so-called "interaction-free'' measurement [Phy s. Rev. Lett. 74 (1995) 4763] is presented, in which the object called "bom b'' is replaced with the atom evolving coherently. It is pointed out that, due to the quantum Zeno effect, the "explosion" symbolized by the absorptio n 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 whi ch now has a highly entangling character. Properties of the new evolution a re discussed. It is also proved that beyond the quantum Zeno effect regime there is a natural possibility of conditional (i.e., followed by the sequen ce of some, but not necessarily frequent. probes) freezing of the evolving system in a maximally entangled state. An explanation of the effects as wel l as some general conclusions are provided.