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Concept
Afshar experiment
Summary
The Afshar experiment is a variation of the double-slit experiment in quantum mechanics, devised and carried out by Shahriar Afshar while at the private, Boston-based Institute for Radiation-Induced Mass Studies (IRIMS). The results were presented at a Harvard seminar in March 2004. Afshar claimed that the experiment gives information about which of two paths a photon takes through the apparatus while simultaneously allowing interference between the two paths to be observed, by showing that a grid of wires, placed at the nodes of the interference pattern, does not alter the beams. Afshar claimed that the experiment violates the principle of complementarity of quantum mechanics, which states roughly that the particle and wave aspects of quantum objects cannot be observed at the same time, and specifically the Englert–Greenberger duality relation. The experiment has been repeated by a number of investigators, but its interpretation is controversial, and there are several theories that explain the effect without violating complementarity.
Afshar's experiment uses a variant of Thomas Young's classic double-slit experiment to create interference patterns to investigate complementarity. One of Afshar's assertions is that, in his experiment, it is possible to check for interference fringes of a photon stream (a measurement of the wave nature of the photons) while at the same time determining each photon's "which-path" information (a measurement of the particle nature of the photons).
In his experiment, pinhole A is correlated to detector 1 when pinhole B is closed, and pinhole B is correlated to detector 2 when pinhole A is closed. Afshar's claim for the violation of the principle of complementarity depends crucially on his assertion that these correlations remain, and thus which-path information is preserved, when both pinholes are open, and cites Wheeler
in support.
Shahriar S. Afshar's experimental work was done initially at the Institute for Radiation-Induced Mass Studies (IRIMS) in Boston in 2001 and later reproduced at Harvard University in 2003, while he was a research scholar there.
Official source
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