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Wheeler's delayed choice experiment is actually several thought experiments in quantum physics, proposed by John Archibald Wheeler, with the most prominent among them appearing in 1978 and 1984.〔''Mathematical Foundations of Quantum Theory'', edited by A.R. Marlow, Academic Press, 1978. P, 39 lists seven experiments: double slit, microscope, split beam, tilt-teeth, radiation pattern, one-photon polarization, and polarization of paired photons.〕 These experiments are attempts to decide whether light somehow "senses" the experimental apparatus in the double-slit experiment it will travel through and adjusts its behavior to fit by assuming the appropriate determinate state for it, or whether light remains in an indeterminate state, neither wave nor particle."〔George Greenstein and Arthur Zajonc, ''The Quantum Challenge'', p. 37f.〕 The common intention of these several types of experiments is to first do something that some interpretations of theory say would make each photon "decide" whether it was 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. Some interpreters of these experiments contend that a photon either is a wave or is a particle, and that it cannot be both at the same time. Wheeler's intent was to investigate the time-related conditions under which a photon makes this transition between alleged states of being. His work has been productive of many revealing experiments. He may not have anticipated the possibility that other researchers would tend toward the conclusion that a photon retains both its "wave nature" and "particle nature" until the time it ends its life, e.g., by being absorbed by an electron which acquires its energy and therefore rises to a higher-energy orbital in its atom. However, he himself seems to be very clear on this point. He says: The thing that causes people to argue about when and how the photon learns that the experimental apparatus is in a certain configuration and then changes from wave to particle to fit the demands of the experiment's configuration is the assumption that a photon had some physical form before the astronomers observed it. Either it was a wave or a particle; either it went both ways around the galaxy or only one way. Actually, quantum phenomena are neither waves nor particles but are intrinsically undefined until the moment they are measured. In a sense, the British philosopher Bishop Berkeley was right when he asserted two centuries ago "to be is to be perceived."〔Scientific American, July 1992, p. 75〕 This line of experimentation proved very difficult to carry out when it was first conceived. Nevertheless, it has proven very valuable over the years since it has led researchers to provide "increasingly sophisticated demonstrations of the wave–particle duality of single quanta."〔Ma, Kofler, Qarry, Tetik, Scheidl, Ursin, Ramelow, Herbst, Ratschbacher, Fedrizzi, Jennewein, and Zeilinger, "Quantum erasure with causally disconnected choice.'' p. 1 (PNAS, January 22, 2013, vol. 110, no. 4, pp. 1221–1226)〕 〔Peruzzo, et al., "A quantum delayed choice experiment," arXiv:1205.4926v2 () 28 Jun 2012. This experiment uses Bell inequalities to replace the delayed choice devices, but it achieves the same experimental purpose in an elegant and convincing way.〕 As one experimenter explains, "Wave and particle behavior can coexist simultaneously." 〔"Entanglement-enabled delayed choice experiment." by Florian Kaiser, Thomas Coudreau, Perola Milman, Daniel B. Ostrowsky, and Sébastien Tanzilli, in arXiv:1206.4348v1〕 ==Introduction== "Wheeler's delayed choice experiment" refers to a series of thought experiments in quantum physics, the first being proposed by him in 1978. Another prominent version was proposed in 1983. All of these experiments try to get at the same fundamental issues in quantum physics. Many of them are discussed in Wheeler's 1978 article, "The 'Past' and the 'Delayed-Choice' Double-Slit Experiment", which has been reproduced in A. R. Marlow's ''Mathematical Foundations of Quantum Theory'', pp. 9–48. According to the complementarity principle, a photon can manifest properties of a particle or of a wave, ''but not both at the same time''. What characteristic is manifested depends on whether experimenters use a device intended to observe particles or to observe waves.〔Edward G. Steward, Quantum Mechanics: Its Early Development and the Road to Entanglement, p. 145〕 When this statement is applied very strictly, one could argue that by determining the detector type one could force the photon to become manifest only as a particle or only as a wave. Detection of a photon is a destructive process because a photon can never be seen in flight. When a photon is detected it "appears" in the consequences of its demise, e.g., by being absorbed by an electron in a photomultiplier that accepts its energy which is then used to trigger the cascade of events that produces a "click" from that device. A photon always appears at some highly localized point in space and time. In the apparatuses that detect photons, the locations on its detection screen that indicate reception of the photon give an indication of whether or not it was manifesting its wave nature during its flight from photon source to the detection device. Therefore it is commonly said that in a double-slit experiment a photon exhibits its wave nature when it passes through both of the slits and appears as a dim wash of illumination across the detection screen, and manifests its particle nature when it passes through only one slit and appears on the screen as a highly localized scintillation. Given the interpretation of quantum physics that says a photon is either in its guise as a wave or in its guise as a particle, the question arises: When does the photon decide whether it is going to travel as a wave or as a particle? Suppose that a traditional double-slit experiment is prepared so that either of the slits can be blocked. If both slits are open and a series of photons are emitted by the laser then an interference pattern will quickly emerge on the detection screen. The interference pattern can only be explained as a consequence of wave phenomena, so experimenters can conclude that each photon "decides" to travel as a wave as soon as it is emitted. If only one slit is available then there will be no interference pattern, so experimenters may conclude that each photon "decides" to travel as a particle as soon as it is emitted. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Wheeler's delayed choice experiment」の詳細全文を読む スポンサード リンク
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