Quantum coherence and interaction-free measurements
  We investigate the extent to which ``interaction-free'' measurements perturb the state of quantum systems. We show that the absence of energy exchange during the measurement is not a sufficient criterion to preserve that state, as the quantum system is subject to measurement dependent decoherence. While it is possible in general to design interaction-free measurement schemes that do preserve that state, the requirement of quantum coherence preservation rapidly leads to a very low efficiency. Our results, which have a simple interpretation in terms of ``which-way'' arguments, open up the way to novel quantum non-demolition techniques. 
S. Potting, E.S. Lee, W. Schmitt, I. Rumyantsev, B. Mohring, P.   Meystre