Editing Double-slit experiment (section)

==Overview==
[[Image:Single slit and double slit2.jpg|right|350px|thumb|Same double-slit assembly (0.7 mm between slits); in top image, one slit is closed. In the single-slit image, a [[diffraction pattern]] (the faint spots on either side of the main band) forms due to the nonzero width of the slit. This diffraction pattern is also seen in the double-slit image, but with many smaller interference fringes.]]
If light consisted strictly of ordinary or [[Classical mechanics|classical]] particles, and these particles were fired in a straight line through a slit and allowed to strike a screen on the other side, we would expect to see a pattern corresponding to the size and shape of the slit. However, when this "single-slit experiment" is actually performed, the pattern on the screen is a [[diffraction pattern]] in which the light is spread out. The smaller the slit, the greater the angle of spread. The top portion of the image shows the central portion of the pattern formed when a red laser illuminates a slit and, if one looks carefully, two faint side bands. More bands can be seen with a more highly refined apparatus. [[Diffraction]] explains the pattern as being the result of the interference of light waves from the slit.

If one illuminates two parallel slits, the light from the two slits again interferes. Here the interference is a more pronounced pattern with a series of alternating light and dark bands. The width of the bands is a property of the frequency of the illuminating light.<ref>[[Charles Sanders Peirce]] first proposed the use of this effect as an artifact-independent reference standard for [[length]]
*C.S. Peirce (July 1879). "Note on the Progress of Experiments for Comparing a Wave-length with a Meter". ''American Journal of Science'', as referenced by Crease, Robert P. (2011). ''World in the Balance: The historic quest for an absolute system of measurement''. New York: W.W. Norton. p. 317. {{ISBN|978-0-393-07298-3}}. p. 203.</ref> (See the bottom photograph to the right.)

[[File:Young diffraction.svg|thumb|Young's drawing of diffraction]]
When [[Thomas Young (scientist)|Thomas Young]] (1773–1829) first demonstrated this phenomenon, it indicated that light consists of waves, as the distribution of brightness can be explained by the alternately additive and subtractive interference of [[wavefront]]s.<ref name="Feynman" /> Young's experiment, performed in the early 1800s, played a crucial role in the understanding of the wave theory of light, vanquishing the [[corpuscular theory of light]] proposed by [[Isaac Newton]], which had been the accepted model of light propagation in the 17th and 18th centuries.

However, the later discovery of the [[photoelectric effect]] demonstrated that under different circumstances, light can behave as if it is composed of discrete particles. These seemingly contradictory discoveries made it necessary to go beyond classical physics and take into account the [[Quantum mechanics|quantum]] nature of light.

Feynman was fond of saying that all of quantum mechanics can be gleaned from carefully thinking through the implications of this single experiment.<ref name="Greene_1999">{{cite book |last= Greene |first= Brian |author-link= Brian Greene |title= The Elegant Universe: Super Strings, Hidden Dimensions, and the Quest for the Ultimate Theory |publisher= W.W. Norton |location= New York |year= 1999 |pages= [https://archive.org/details/elegantuniverses0000gree/page/97 97–109] |isbn= 978-0-393-04688-5 |url= https://archive.org/details/elegantuniverses0000gree/page/97 }}</ref> He also proposed (as a thought experiment) that if detectors were placed before each slit, the interference pattern would disappear.<ref>Feynman, 1965, chapter 3</ref>

The [[Englert–Greenberger duality relation]] provides a detailed treatment of the mathematics of double-slit interference in the context of quantum mechanics.

A low-intensity double-slit experiment was first performed by [[Geoffrey Ingram Taylor|G. I. Taylor]] in 1909,<ref>{{cite journal
| first1=G. I. |last1=Taylor | authorlink1=Geoffrey Ingram Taylor
| title=Interference Fringes with Feeble Light
| journal = [[Mathematical Proceedings of the Cambridge Philosophical Society]]
| volume=15
| page=114
| date=1909
| url=https://archive.org/details/proceedingsofcam15190810camb/page/114/mode/2up | access-date=7 December 2024}}</ref> by reducing the level of incident light until photon emission/absorption events were mostly non-overlapping.
{{Anchor|Claus Jönsson}}
A slit interference experiment was not performed with anything other than light until 1961, when [[Claus Jönsson]] of the [[University of Tübingen]] performed it with coherent electron beams and multiple slits.<ref>{{Cite journal|last=Jönsson|first=Claus|date=1 August 1961|title=Elektroneninterferenzen an mehreren künstlich hergestellten Feinspalten|journal=Zeitschrift für Physik|language=de|volume=161|issue=4|pages=454–474|doi=10.1007/BF01342460|issn=0044-3328|bibcode = 1961ZPhy..161..454J |s2cid=121659705}}</ref><ref>{{Cite journal|last=Jönsson|first=Claus|date=1 January 1974|title=Electron Diffraction at Multiple Slits|journal=American Journal of Physics|volume=42|issue=1|pages=4–11|doi=10.1119/1.1987592|issn=0002-9505|bibcode = 1974AmJPh..42....4J }}</ref> In 1974, the Italian physicists Pier Giorgio Merli, Gian Franco Missiroli, and [[Giulio Pozzi]] performed a related experiment using single electrons from a coherent source and a biprism beam splitter, showing the statistical nature of the buildup of the interference pattern, as predicted by quantum theory.<ref>{{cite journal |last1= Merli |first1= P G |last2= Missiroli |first2= G F |last3= Pozzi |first3= G |year= 1976 |title= On the statistical aspect of electron interference phenomena |journal= American Journal of Physics |volume= 44 |issue= 3|pages= 306–307 |doi= 10.1119/1.10184 |bibcode = 1976AmJPh..44..306M}}</ref><ref>{{cite journal |last1= Rosa |first1= R |year= 2012 |title= The Merli–Missiroli–Pozzi Two-Slit Electron-Interference Experiment |journal = Physics in Perspective |volume= 14 |issue= 2| pages= 178–194 |doi= 10.1007/s00016-011-0079-0 |pmid= 26525832 |pmc= 4617474 |bibcode = 2012PhP....14..178R }}</ref> In 2002, the single-electron version of the experiment was voted "the most beautiful experiment" by readers of ''[[Physics World]].''<ref>[https://physicsworld.com/a/the-double-slit-experiment/ "The most beautiful experiment"]. Physics World 2002 {{Webarchive|url=https://web.archive.org/web/20210524080643/https://physicsworld.com/a/the-double-slit-experiment/ |date=24 May 2021 }}</ref> Since that time a number of related experiments have been published, with a little controversy.<ref>{{Cite journal |last1=Steeds |first1=John |last2=Merli |first2=Pier Giorgio |last3=Pozzi |first3=Giulio |last4=Missiroli |first4=GianFranco |last5=Tonomura |first5=Akira |date=2003 |title=The double-slit experiment with single electrons |url=https://iopscience.iop.org/article/10.1088/2058-7058/16/5/24 |journal=Physics World |volume=16 |issue=5 |pages=20–21 |doi=10.1088/2058-7058/16/5/24 |issn=0953-8585}}</ref>

In 2012, Stefano Frabboni and co-workers sent single electrons onto nanofabricated slits (about 100&nbsp;nm wide) and, by detecting the transmitted electrons with a single-electron detector, they could show the build-up of a double-slit interference pattern.<ref>{{Cite journal|last1=Frabboni|first1=Stefano|last2=Gabrielli|first2=Alessandro|last3=Carlo Gazzadi|first3=Gian|last4=Giorgi|first4=Filippo|last5=Matteucci|first5=Giorgio|last6=Pozzi|first6=Giulio|last7=Cesari|first7=Nicola Semprini|last8=Villa|first8=Mauro|last9=Zoccoli|first9=Antonio|date=May 2012|title=The Young-Feynman two-slits experiment with single electrons: Build-up of the interference pattern and arrival-time distribution using a fast-readout pixel detector|journal=Ultramicroscopy|volume=116|pages=73–76|doi=10.1016/j.ultramic.2012.03.017|issn=0304-3991}}</ref> Many related experiments involving the coherent interference have been performed; they are the basis of modern electron diffraction, microscopy and high resolution imaging.<ref>{{Cite book |last=Cowley |first=J. M. |title=Diffraction physics |date=1995 |publisher=Elsevier |isbn=978-0-444-82218-5 |edition=3rd |series=North Holland personal library |location=Amsterdam}}</ref><ref>{{Cite book |last=Spence |first=John C. H. |title=High-resolution electron microscopy |date=2017 |publisher=Oxford University Press |isbn=978-0-19-879583-4 |edition=Fourth edition, first published in paperback |location=Oxford}}</ref>

In 2018, single particle interference was demonstrated for antimatter in the [https://www.positron.fisi.polimi.it/ Positron Laboratory] (L-NESS, [[Politecnico di Milano]]) of Rafael Ferragut<!--Q53261781--> in [[Como]] ([[Italy]]), by a group led by Marco Giammarchi.<ref>{{cite journal | doi = 10.1126/sciadv.aav7610 | volume=5 | title=First demonstration of antimatter wave interferometry | year=2019 | journal=Science Advances | page=eaav7610 | last1 = Sala | first1 = S. | last2 = Ariga | first2 = A. | last3 = Ereditato | first3 = A. | last4 = Ferragut | first4 = R. | last5 = Giammarchi | first5 = M. | last6 = Leone | first6 = M. | last7 = Pistillo | first7 = C. | last8 = Scampoli | first8 = P. | issue=5 | pmid = 31058223 | pmc = 6499593 | bibcode = 2019SciA....5.7610S}}</ref>