Experimental realization of Wheeler's delayed-choice GedankenExperiment

Vincent Jacques (1) , E. Wu (1, 2) , Frédéric Grosshans (1) , François Treussart (1) , Philippe Grangier (3) , Alain Aspect (4) , Jean-François Roch (1)

1 LPQM - Laboratoire de Photonique Quantique et Moléculaire
2 Key Laboratory of Optical and Magnetic Resonance Spectroscopy
3 Laboratoire Charles Fabry de l'Institut d'Optique / Optique quantique
4 laboratoire Charles Fabry de l'Institut d'Optique / Optique atomique

The quantum "mystery which cannot go away" (in Feynman's words) of wave-particle duality is illustrated in a striking way by Wheeler's delayed-choice GedankenExperiment. In this experiment, the configuration of a two-path interferometer is chosen after a single-photon pulse has entered it : either the interferometer is \textit{closed} (\textit{i.e.} the two paths are recombined) and the interference is observed, or the interferometer remains \textit{open} and the path followed by the photon is measured. We report an almost ideal realization of that GedankenExperiment, where the light pulses are true single photons, allowing unambiguous which-way measurements, and the interferometer, which has two spatially separated paths, produces high visibility interference. The choice between measuring either the 'open' or 'closed' configuration is made by a quantum random number generator, and is space-like separated -- in the relativistic sense -- from the entering of the photon into the interferometer. Measurements in the closed configuration show interference with a visibility of 94%, while measurements in the open configuration allow us to determine the followed path with an error probability lower than 1%.

Domaines: Physique Quantique [quant-ph]

Vincent Jacques, E. Wu, Frédéric Grosshans, François Treussart, Philippe Grangier, et al.. Experimental realization of Wheeler's delayed-choice GedankenExperiment. Science, 2007, 315 (5814), pp.966. ⟨10.1126/science.1136303⟩. ⟨hal-00110392⟩