Interaction-free measurement with an imperfect absorber
  In this paper, we consider interaction-free measurement (IFM) with imperfect interaction. In the IFM proposed by Kwiat et al., we assume that interaction between an absorbing object and a probe photon is imperfect, so that the photon is absorbed with probability 1-\eta (0\leq\eta\leq 1) and it passes by the object without being absorbed with probability \eta when it approaches close to the object. We derive the success probability P that we can find the object without the photon absorbed under the imperfect interaction as a power series in 1/N, and show the following result: Even if the interaction between the object and the photon is imperfect, we can let the success probability P of the IFM get close to unity arbitrarily by making the reflectivity of the beam splitter larger and increasing the number of the beam splitters. Moreover, we obtain an approximating equation of P for large N from the derived power series in 1/N. 
Hiroo Azuma