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Science. 2007 Feb 16;315(5814):966-8.

Experimental realization of Wheeler's delayed-choice gedanken experiment.

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  • 1Laboratoire de Photonique Quantique et MolĂ©culaire, Ecole Normale SupĂ©rieure de Cachan, UMR CNRS 8537, 94235 Cachan, France.


Wave-particle duality is strikingly illustrated by Wheeler's delayed-choice gedanken experiment, where the configuration of a two-path interferometer is chosen after a single-photon pulse has entered it: Either the interferometer is closed (that is, the two paths are recombined) and the interference is observed, or the interferometer remains open and the path followed by the photon is measured. We report an almost ideal realization of that gedanken experiment with single photons allowing unambiguous which-way measurements. The choice between open and closed configurations, made by a quantum random number generator, is relativistically separated from the entry of the photon into the interferometer.

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