title: Experimental realization of Wheeler's delayed-choice gedanken experiment.
abstract: 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.
authors.affiliation: Laboratoire de Photonique Quantique et Moléculaire, Ecole Normale Supérieure de Cachan, UMR CNRS 8537, 94235 Cachan, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Jacques
authors.forename: E
authors.initials: E
authors.lastname: Wu
authors.forename: Frédéric
authors.initials: F
authors.lastname: Grosshans
authors.forename: François
authors.initials: F
authors.lastname: Treussart
authors.forename: Philippe
authors.initials: P
authors.lastname: Grangier
authors.forename: Alain
authors.initials: A
authors.lastname: Aspect
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Roch