The original theorems of Bell and of Greenberger, Horne, and Zeilinger (GHZ) are extended from ideal to real situations using an intuitive and straightforward approach. This alternative derivation has the merit of showing that if a theorem is valid whenever we have perfect correlations, it cannot be totally wrong in the case of almost perfect correlations. Therefore, it is probably easy (i.e., by introducing only small changes in the original argument) to extend the result to deal with imperfect correlations.
We propose an experiment that permits observation of the de Broglie two-photon wave packet behavior for a pair of photons, using a Mach-Zehnder interferometer. It is based on the use of pulsed lasers to generate pairs of photons via spontaneous parametric down-conversion and the post-selection of events. It differs from previous realizations by the use of a third time-correlated photon to engineer the state of the photons. The same technique can give us which-path information via an ''interaction-free'' experiment and can be used in other experiments on the foundations of quantum mechanics related to wave-particle duality and to nonlocality.
It has been shown in experiments on induced coherence without induced emission using two coherently pumped nonlinear crystals that (a) no second-order interference occurs as long as it is possible, even if only in principle, to determine which of the two crystals emitted the photon pair; (b) second-order interference does occur whenever it is intrinsically impossible to determine which of the two crystals emitted the photon pair. The present paper discusses a variant of the previous experiments in which, apparently, (c) each photon of the pair is emitted by a different crystal. It is also shown that interference is not necessarily reduced when there is no intrinsic indistinguishability.The experiment provides a proof of Bell's theorem for two particles without using an inequality and, at least in principle, could be used to test local realism against quantum mechanics.However, as in the case of the other experiments so far performed, some additional assumption would have to be introduced. It is then shown that the introduction of a reasonable assumption reduces the detectors's efficiencies needed to test local realism, even if nonenhancement is not assumed.PACS number(s): 03.65. Bz, 42.50.Dv Experiments in which interference is observed in the superposition of signal photons from two coherently pumped parametric down-converters have been reported by Mandel and co-workers [I]. It has been shown that no interference occurs as long as it is possible to determine which of the two crystals emitted the photon pair. It does not matter whether we have or do not have the practical means to distinguish which of the two crystals emitted the photons. If it is possible in principle, no interference will be observed. It has also been shown that interference does occur whenever it is intrinsically impossible to determine which of the two crystals emitted the photon pair. In the present paper, I wish to discuss a variant of these previous experiments. In this experiment, apparently, each photon of the pair is emitted by a different crystal, and it is possible to determine which of the two crystals emitted the idler and which emitted the signal. A situation is also discussed in which interference is not reduced even though there is no intrinsic indistinguishability.That is, in some cases it is possible to determine which of the two crystals emitted the photon pair. Although at first sight this should correspond to a reduction in the interference, it in fact does not. As we will also see, there is a sort of conservation of information. The information gained about the photons emitted by one of the crystals is compensated by a loss of information about the photons emitted by the other crystal. In other words: whenever it is possible to determine which of the two crystals emitted the photon pair, one possibility is actualized, so to speak, and no interference is observed. On the other hand, whenever it is not possible to determine which of the two crystals emitted the photon pair, two possibilities are actualized, and interferenc...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.