Fundamental limit on "interaction-free" measurements - art. no. 052103

In "interaction-free" measurements, one typically wants to detect the prese nce of an object without touching it with even a single photon. One often i magines a bomb whose trigger is an extremely sensitive measuring device who se presence we would like to detect without triggering it. We point out tha t all such measuring devices have a maximum sensitivity set by the uncertai nty principle, and thus can only determine whether a measurement is "intera ction-free'' to within a finite minimum resolution. We further discuss exac tly what can be achieved with the proposed "interaction-free" measurement s chemes.