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Why the Afshar experiment does not refute complementarity. (English) Zbl 1222.81278

Summary: A modified version of Young’s experiment by Shahriar Afshar demonstrates that, prior to what appears to be a “which-way” measurement, an interference pattern exists. Afshar has claimed that this result constitutes a violation of the Principle of Complementarity. This paper discusses the implications of this experiment and considers how Cramer’s Transactional Interpretation easily accommodates the result. It is also shown that the Afshar experiment is analogous in key respects to a spin one-half particle prepared as “spin up along \(x\)”, subjected to a nondestructive confirmation of that preparation, and post-selected in a specific state of spin along \(z\). The terminology “which-way” or “which-slit” is critiqued; it is argued that this usage by both Afshar and his critics is misleading and has contributed to confusion surrounding the interpretation of the experiment. Nevertheless, it is concluded that Bohr would have had no more problem accounting for the Afshar result than he would in accounting for the aforementioned pre- and post-selection spin experiment, in which the particle’s preparation state is confirmed by a nondestructive measurement prior to post-selection. In addition, some new inferences about the interpretation of delayed choice experiments are drawn from the analysis.

MSC:

81T99 Quantum field theory; related classical field theories
81-03 History of quantum theory
81P05 General and philosophical questions in quantum theory

References:

[1] Afshar, S. (2004). Sharp complementary wave and particle behaviors in the same welcher weg experiment. E-print: www.irims.org/quant-ph/030503; Afshar, S. (2004). Sharp complementary wave and particle behaviors in the same welcher weg experiment. E-print: www.irims.org/quant-ph/030503
[2] Aharonov, Y.; Bergmann, P.; Lebowitz, J., Time symmetry in the quantum process of measurement, Physical Review B, 134, 1410-1416 (1964) · Zbl 0127.43703
[3] Albert, D.; Aharonov, Y.; D’Amato, S., Curious new statistical prediction of quantum mechanics, Physical Review Letters, 54, 5-7 (1985)
[4] Cramer, J. G., The transactional interpretation of quantum mechanics, Reviews of Modern Physics, 58, 647-688 (1986)
[5] Unruh, W. (2004). Shahriar Afshar—quantum rebel? E-print: axion.physics.ubc.ca/rebel.html.; Unruh, W. (2004). Shahriar Afshar—quantum rebel? E-print: axion.physics.ubc.ca/rebel.html.
[6] Wheeler, J. A., 1981. Delayed-choice experiments and the Bohr-Einstein dialogue. Originally published in The American Philosophical Society and The Royal SocietyPapers read at a meetingJune 5, 1980Quantum theory and measurement; Wheeler, J. A., 1981. Delayed-choice experiments and the Bohr-Einstein dialogue. Originally published in The American Philosophical Society and The Royal SocietyPapers read at a meetingJune 5, 1980Quantum theory and measurement
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