"A quantum delayed choice experiment" in "Science".

Alberto Peruzzo, Peter J. Shadbolt, Nicolas Brunner, Sandu Popescu, Jeremy L. O'Brien. "A quantum delayed choice experiment" in "Science" 2 November 2012, American Association for the Advancement of Science, vol 338 no. 6107, pp 634-637 in the full weekly issue. Bound with in this same issue: Florian Kaiser et al., "Entangled-Enabled Delayed-Choice Experiment", pp 637-640. Original wrappers. FINE copy. "Quantum systems exhibit particle-like or wave-like behaviour depending on the experimental apparatus they are confronted by. This wave-particle duality is at the heart of quantum mechanics, and is fully captured in Wheeler's* famous delayed choice gedanken experiment. In this variant of the double slit experiment, the observer chooses to test either the particle or wave nature of a photon after it has passed through the slits. Here we report on a quantum delayed choice experiment, based on a quantum controlled beam-splitter, in which both particle and wave behaviours can be investigated simultaneously. The genuinely quantum nature of the photon's behaviour is tested via a Bell inequality, which here replaces the delayed choice of the observer. We observe strong Bell inequality violations, thus showing that no model in which the photon knows in advance what type of experiment it will be confronted by, hence behaving either as a particle or as wave, can account for the experimental data."--Arxiv (via Cornell University) abstract. [++] "This wave-particle duality is at the heart of quantum mechanics. Its paradoxical nature is best captured in the delayed-choice thought experiment, in which a photon is forced to choose a behavior before the observer decides what to measure."--Wikipedia [++] *John Archibald Wheeler, "The 'Past' and the 'Delayed-Choice Double-Slit Experiment'," in A.R. Marlow, editor, Mathematical Foundations of Quantum Theory, Academic Press (1978), pp 9 48. "The common intention of these several types of experiments is to first do something that, according to some hidden-variable models,  would make each photon "decide" whether it were going to behave as a particle or behave as a wave, and then, before the photon had time to reach the detection device, create another change in the system that would make it seem that the photon had "chosen" to behave in the opposite way. "--Wikipedia.