Interaction-Free Measurement of a Quantum Object: On the Breeding of “Schrödinger Cats”

  • Paul G. Kwiat
  • Harald Weinfurter
  • Anton Zeilinger


The possibility of an “interaction-free” determination of the presence of an object was first discussed by Renninger and by Dicke,1 who examined the effect on a quantum system due to the non-observation of a particular result (e.g., the non-scattering of a photon). Elitzur and Vaidman extended these ideas, so that the presence of an object modified the interference of a photon, even though the photon and object need not have interacted.2 In the best case, their method works only 50% of the time. We have recently reported a different technique,3 based on the quantum Zeno effect,4 which allows the fraction of interaction-free measurements (IFMs) to be arbitrarily close to 1. As a result, one even has the possibility to employ multi-photon pulses for the interrogation. When the object being observed is in a quantum superposition state, one can prepare superpositions and entanglements of these macroscopic states of light.


Coherent State Entangle State Quantum Object Macroscopic State Coupling Path 
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Copyright information

© Springer Science+Business Media New York 1996

Authors and Affiliations

  • Paul G. Kwiat
    • 1
  • Harald Weinfurter
    • 1
  • Anton Zeilinger
    • 1
  1. 1.Institut für ExperimentalphysikUniversität InnsbruckInnsbruckAustria

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