Afshar experiment

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The Afshar experiment is a variation of the double-slit experiment in quantum mechanics, devised and carried out by Shahriar Afshar in 2004. [1] [2] In the experiment, light generated by a laser passes through two closely spaced pinholes, and is refocused by a lens so that the image of each pinhole falls on a separate single-photon detector. In addition, a grid of thin wires is placed just before the lens on the dark fringes of an interference pattern. [3]

Contents

Afshar claimed that the experiment gives information about which path a photon takes through the apparatus, while simultaneously allowing interference between the paths to be observed. [4] [5] According to Afshar, this violates the complementarity principle of quantum mechanics. [3] [6]

The experiment has been analyzed and repeated by a number of investigators. [7] There are several theories that explain the effect without violating complementarity. [8] [9] [10] [11] John G. Cramer claims the experiment provides evidence for the transactional interpretation of quantum mechanics over other interpretations.

History

Shahriar Afshar's experimental work was done initially at the Institute for Radiation-Induced Mass Studies (IRIMS) [12] in Boston and later reproduced at Harvard University, while he was there as a visiting researcher. [1] The results were first presented at a seminar at Harvard in March 2004. [2] The experiment was featured as the cover story in the July 24, 2004 edition of the popular science magazine New Scientist endorsed by professor John G. Cramer of the University of Washington. [1] [13] The New Scientist feature article generated many responses, including various letters to the editor that appeared in the August 7 and August 14, 2004 issues, arguing against the conclusions being drawn by Afshar. [14] The results were published in a SPIE conference proceedings in 2005. [4] A follow-up paper was published in a scientific journal Foundations of Physics in January 2007 [3] and featured in New Scientist in February 2007. [15]

Experimental setup

Fig.1 Experiment without obstructing wire grid Afshar-experiment.png
Fig.1 Experiment without obstructing wire grid
Fig.2 Experiment with obstructing wire grid and one pinhole covered Afshar-experiment-wire.png
Fig.2 Experiment with obstructing wire grid and one pinhole covered
Fig.3 Experiment with wire grid and both pinholes open. The wires lie in the dark fringes and thus block very little light Afshar-experiment-1.png
Fig.3 Experiment with wire grid and both pinholes open. The wires lie in the dark fringes and thus block very little light

The experiment uses a setup similar to that for the double-slit experiment. In Afshar's variant, light generated by a laser passes through two closely spaced circular pinholes (not slits). After the dual pinholes, a lens refocuses the light so that the image of each pinhole falls on separate photon-detectors (Fig. 1). With pinhole 2 closed, a photon that goes through pinhole 1 impinges only on photon detector 1. Similarly, with pinhole 1 closed, a photon that goes through pinhole 2 impinges only on photon detector 2. With both pinholes open, Afshar claims, citing Wheeler [16] in support, that pinhole 1 remains correlated to photon Detector 1 (and vice versa for pinhole 2 to photon Detector 2), and therefore that which-way information is preserved when both pinholes are open. [3]

When the light acts as a wave, because of quantum interference one can observe that there are regions that the photons avoid, called dark fringes. A grid of thin wires is placed just before the lens (Fig. 2) so that the wires lie in the dark fringes of an interference pattern which is produced by the dual pinhole setup. If one of the pinholes is blocked, the interference pattern will no longer be formed, and the grid of wires causes appreciable diffraction in the light and blocks some of it from detection by the corresponding photon detector. However, when both pinholes are open, the effect of the wires is negligible, comparable to the case in which there are no wires placed in front of the lens (Fig. 3), because the wires lie in the dark fringes of an interference pattern. The effect is not dependent on the light intensity (photon flux).

Afshar's interpretation

Afshar's conclusion is that, when both pinholes are open, the light exhibits wave-like behavior when going past the wires, since the light goes through the spaces between the wires but avoids the wires themselves, but also exhibits particle-like behavior after going through the lens, with photons going to a correlated photo-detector. Afshar argues that this behavior contradicts the principle of complementarity to the extent that it shows both wave and particle characteristics in the same experiment for the same photons.

Afshar asserts that there is simultaneously high visibility V of interference as well as high distinguishability D (corresponding to which-path information), so that V2 + D2 > 1, and the wave-particle duality relation is violated. [3]

Reception

Specific criticism

A number of scientists have published criticisms of Afshar's interpretation of his results, some of which reject the claims of a violation of complementarity, while differing in the way they explain how complementarity copes with the experiment. For example, one paper contests Afshar's core claim, that the Englert–Greenberger duality relation is violated. The researchers re-ran the experiment, using a different method for measuring the visibility of the interference pattern than that used by Afshar, and found no violation of complementarity, concluding "This result demonstrates that the experiment can be perfectly explained by the Copenhagen interpretation of quantum mechanics." [10]

Below is a synopsis of papers by several critics highlighting their main arguments and the disagreements they have amongst themselves:

Specific support

See also

Related Research Articles

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References

  1. 1 2 3 Chown, Marcus (2004). "Quantum Rebel". New Scientist . 183 (2457): 30–35.(subscription required)
  2. 1 2 S. S. Afshar (2004). "Waving Copenhagen Good-bye: Were the founders of Quantum Mechanics wrong?". Harvard Seminar Announcement. Archived from the original on 2012-03-05. Retrieved 2013-12-01.
  3. 1 2 3 4 5 S. S. Afshar; E. Flores; K. F. McDonald; E. Knoesel (2007). "Paradox in wave-particle duality". Foundations of Physics . 37 (2): 295–305. arXiv: quant-ph/0702188 . Bibcode:2007FoPh...37..295A. doi:10.1007/s10701-006-9102-8. S2CID   2161197.
  4. 1 2 S. S. Afshar (2005). Roychoudhuri, Chandrasekhar; Creath, Katherine (eds.). "Violation of the principle of complementarity, and its implications". Proceedings of SPIE . The Nature of Light: What Is a Photon?. 5866: 229–244. arXiv: quant-ph/0701027 . Bibcode:2005SPIE.5866..229A. doi:10.1117/12.638774. S2CID   119375418.
  5. ↑ S. S. Afshar (2006). "Violation of Bohr's complementarity: One slit or both?". AIP Conference Proceedings . 810: 294–299. arXiv: quant-ph/0701039 . Bibcode:2006AIPC..810..294A. doi:10.1063/1.2158731. S2CID   117905639.
  6. ↑ J. Zheng; C. Zheng (2011). "Variant simulation system using quaternion structures". Journal of Modern Optics . 59 (5): 484. Bibcode:2012JMOp...59..484Z. doi:10.1080/09500340.2011.636152. S2CID   121934786.
  7. ↑ Georgiev, Danko (2012-01-26). "Quantum Histories and Quantum Complementarity". ISRN Mathematical Physics. 2012: 1–37. doi: 10.5402/2012/327278 . ISSN   2090-4681.
  8. 1 2 R. Kastner (2005). "Why the Afshar experiment does not refute complementarity?". Studies in History and Philosophy of Modern Physics . 36 (4): 649–658. arXiv: quant-ph/0502021 . Bibcode:2005SHPMP..36..649K. doi:10.1016/j.shpsb.2005.04.006. S2CID   119438183.
  9. 1 2 O. Steuernagel (2007). "Afshar's experiment does not show a violation of complementarity". Foundations of Physics . 37 (9): 1370. arXiv: quant-ph/0512123 . Bibcode:2007FoPh...37.1370S. doi:10.1007/s10701-007-9153-5. S2CID   53056142.
  10. 1 2 V. Jacques; et al. (2008). "Illustration of quantum complementarity using single photons interfering on a grating". New Journal of Physics . 10 (12): 123009. arXiv: 0807.5079 . Bibcode:2008NJPh...10l3009J. doi:10.1088/1367-2630/10/12/123009. S2CID   2627030.
  11. ↑ D. D. Georgiev (2012). "Quantum histories and quantum complementarity". ISRN Mathematical Physics. 2012: 327278. doi: 10.5402/2012/327278 .
  12. ↑ "Institute for Radiation-Induced Mass Studies (IRIMS)". irims.org. Retrieved 2023-09-21.
  13. ↑ Afshar's Quantum Bomshell [ permanent dead link ] Science Friday
  14. ↑ J. G. Cramer (2004). "Bohr is still wrong". New Scientist . 183 (2461): 26.
  15. ↑ Chown, Marcus (2007). "Quantum rebel wins over doubters". New Scientist . 197 (2591): 13.(subscription required)
  16. ↑ Wheeler, John (1978). Mathematical foundations of quantum theory. Elsevier. pp. 9–48.
  17. ↑ R. E. Kastner (2006). "The Afshar Experiment and Complementarity". APS Meeting, March 13–17, Baltimore, Maryland: 40011. Bibcode:2006APS..MARD40011K.
  18. ↑ D. Reitzner (2007). "Comment on Afshar's experiments". arXiv: quant-ph/0701152 . Bibcode:2007quant.ph..1152R.{{cite journal}}: Cite journal requires |journal= (help)
  19. ↑ W. Unruh (2004). "Shahriar Afshar – Quantum Rebel?".
  20. ↑ L. Motl (2004). "Violation of complementarity?".
  21. ↑ Andrew Knight (2020). "No Paradox in Wave-Particle Duality". Foundations of Physics . 50 (11): 1723–1727. arXiv: 2006.05315 . Bibcode:2020FoPh...50.1723K. doi:10.1007/s10701-020-00379-9. S2CID   219559143.
  22. ↑ E. Flores and E. Knoesel (2007). "Why Kastner analysis does not apply to a modified Afshar experiment". In Roychoudhuri, Chandrasekhar; Kracklauer, Al F; Creath, Katherine (eds.). The Nature of Light: What Are Photons?. Vol. 6664. pp. 66640O. arXiv: quant-ph/0702210 . doi:10.1117/12.730965. S2CID   119028739.
  23. ↑ J. G. Cramer (2005). "A farewell to Copenhagen?". Analog Science Fiction and Fact . Archived from the original on 2004-12-08. Retrieved 2004-12-21.
  24. ↑ Cramer, JG (2015). The Quantum Handshake: Entanglement, Nonlocality and Transactions. Springer Verlag. pp. 111–112. ISBN   978-3-319-24642-0.
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