Editing Double-slit experiment (section)

===Other variations===
[[File:Double-slit wall sm.jpg|thumb|A laboratory double-slit assembly; distance between top posts is approximately 2.5&nbsp;cm (one inch).]]
[[File:Plasmonic Young's double slits interference.png|thumb|Near-field intensity distribution patterns for plasmonic slits with equal widths (A) and non-equal widths (B).]]

In 1967, Pfleegor and Mandel demonstrated two-source interference using two separate lasers as light sources.<ref>{{cite journal | journal=[[Physical Review]] | title=Interference of Independent Photon Beams |author1=Pfleegor, R. L.  |author2=Mandel, L. | date=July 1967 | volume=159 | issue=5 | pages=1084–1088 | doi=10.1103/PhysRev.159.1084|bibcode = 1967PhRv..159.1084P }}</ref><ref>{{cite web |url=http://scienceblogs.com/principles/2010/11/interference_of_independent_ph.php |title=Interference of Independent Photon Beams: The Pfleegor-Mandel Experiment|access-date=16 June 2011 |archive-url=https://web.archive.org/web/20110103104840/http://scienceblogs.com/principles/2010/11/interference_of_independent_ph.php |archive-date=3 January 2011  }}></ref>

It was shown experimentally in 1972 that in a double-slit system where only one slit was open at any time, interference was nonetheless observed provided the path difference was such that the detected photon could have come from either slit.<ref>{{cite journal | title=An interference experiment with light beams modulated in anti-phase by an electro-optic shutter |author1=Sillitto, R.M.  |author2=Wykes, Catherine | journal=Physics Letters A | year=1972 | volume=39 | issue=4 | pages=333–334 | doi=10.1016/0375-9601(72)91015-8|bibcode = 1972PhLA...39..333S }}</ref><ref>{{cite web| url = http://www.sillittopages.co.uk/80rms_35.html| title = "To a light particle"}}</ref> The experimental conditions were such that the photon density in the system was much less than 1.

In 1991, Carnal and Mlynek performed the classic Young's double slit experiment with [[Metastability|metastable]] helium atoms passing through micrometer-scale slits in gold foil.<ref>{{cite journal | journal=[[Physical Review Letters]] | title=Young's Double-Slit Experiment with Atoms: A Simple Atom Interferometer |author1=Carnal, O. |author2=Mlynek, J. | date=May 1991 | volume=66 | number=21 | pages=2689–2694 | doi=10.1103/PhysRevLett.66.2689| pmid=10043591 | bibcode=1991PhRvL..66.2689C | url=http://elib.bsu.by/handle/123456789/154548 }}</ref><ref>{{cite journal |url=https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.66.2689 |title=Young's Double-Slit Experiment with Atoms: A Simple Atom Interferometer|date=1991 |doi=10.1103/PhysRevLett.66.2689 |pmid=10043591 |access-date=20 March 2022 |last1=Carnal |first1=O. |last2=Mlynek |first2=J. |journal=Physical Review Letters |volume=66 |issue=21 |pages=2689–2692 |bibcode=1991PhRvL..66.2689C }}></ref>

In 1999, a quantum interference experiment (using a diffraction grating, rather than two slits) was successfully performed with buckyball molecules (each of which comprises 60 carbon atoms).<ref name="buckyballs">[https://www.newscientist.com/article/mg20627596.100-quantum-wonders-corpuscles-and-buckyballs.html New Scientist: Quantum wonders: Corpuscles and buckyballs, 2010] (Introduction, subscription needed for full text, quoted in full in [http://postbiota.org/pipermail/tt/2010-May/007336.html] {{Webarchive|url=https://web.archive.org/web/20170925163808/http://postbiota.org/pipermail/tt/2010-May/007336.html|date=25 September 2017}})</ref><ref>{{Cite journal |doi = 10.1038/44348|title = Wave–particle duality of C60 molecules|journal = Nature|volume = 401|issue = 6754|pages = 680–682|year = 1999|last1 = Arndt|first1 = Markus|last2 = Nairz|first2 = Olaf|last3 = Vos-Andreae|first3 = Julian|last4 = Keller|first4 = Claudia|last5 = Van Der Zouw|first5 = Gerbrand|last6 = Zeilinger|first6 = Anton|bibcode = 1999Natur.401..680A|pmid = 18494170|s2cid = 4424892}}</ref> A buckyball is large enough (diameter about 0.7&nbsp;[[Nanometre|nm]], nearly half a million times larger than a proton) to be seen in an [[electron microscope]].

In 2002, an electron field emission source was used to demonstrate the double-slit experiment. In this experiment, a coherent electron wave was emitted from two closely located emission sites on the needle apex, which acted as double slits, splitting the wave into two coherent electron waves in a vacuum. The interference pattern between the two electron waves could then be observed.<ref>{{Cite journal |last1=Oshima |first1=C. |last2=Mastuda |first2=K. |last3=Kona |first3=T. |last4=Mogami |first4=Y. |last5=Komaki |first5=M. |last6=Murata |first6=Y. |last7=Yamashita |first7=T. |last8=Kuzumaki |first8=T. |last9=Horiike |first9=Y. |date=2002-01-04 |title=Young's Interference of Electrons in Field Emission Patterns |url=https://link.aps.org/doi/10.1103/PhysRevLett.88.038301 |journal=Physical Review Letters |language=en |volume=88 |issue=3 |page=038301 |doi=10.1103/PhysRevLett.88.038301 |pmid=11801091 |bibcode=2002PhRvL..88c8301O |issn=0031-9007}}</ref> In 2017, researchers performed the double-slit experiment using light-induced field electron emitters. With this technique, emission sites can be optically selected on a scale of ten nanometers. By selectively deactivating (closing) one of the two emissions (slits), researchers were able to show that the interference pattern disappeared.<ref>{{Cite journal |last1=Yanagisawa |first1=Hirofumi |last2=Ciappina |first2=Marcelo |last3=Hafner |first3=Christian |last4=Schötz |first4=Johannes |last5=Osterwalder |first5=Jürg |last6=Kling |first6=Matthias F. |date=2017-10-04 |title=Optical Control of Young's Type Double-slit Interferometer for Laser-induced Electron Emission from a Nano-tip |journal=Scientific Reports |language=en |volume=7 |issue=1 |page=12661 |doi=10.1038/s41598-017-12832-3 |issn=2045-2322 |pmc=5627254 |pmid=28978914|arxiv=1710.02216 |bibcode=2017NatSR...712661Y }}</ref>

In 2005, E. R. Eliel presented an experimental and theoretical study of the optical transmission of a thin metal screen perforated by two subwavelength slits, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or enhanced as a function of the wavelength of the incident light beam.<ref>{{cite journal|last1=Schouten|first1=H.F.|last2=Kuzmin|first2=N.|last3=Dubois|first3=G.|last4=Visser|first4=T.D.|last5=Gbur|first5=G.|last6=Alkemade|first6=P.F.A.|last7=Blok|first7=H.|last8=Hooft|first8=G.W.|last9=Lenstra|first9=D.|last10=Eliel|first10=E.R.|title=Plasmon-Assisted Two-Slit Transmission: Young's Experiment Revisited|journal=Phys. Rev. Lett.|date=7 February 2005|volume=94|issue=5|page=053901|doi=10.1103/physrevlett.94.053901|bibcode = 2005PhRvL..94e3901S|pmid=15783641|hdl=1887/71482|s2cid=19197175 |url=http://repository.tudelft.nl/islandora/object/uuid%3Abe5f0a85-ad6e-40ac-a8f3-2028a2c235c8/datastream/OBJ/view|author5-link=Greg Gbur|hdl-access=free}}<!--|access-date=7 February 2007--></ref>

In 2012, researchers at the [[University of Nebraska–Lincoln]] performed the double-slit experiment with electrons as described by [[Richard Feynman]], using new instruments that allowed control of the transmission of the two slits and the monitoring of single-electron detection events.  Electrons were fired by an electron gun and passed through one or two slits of 62&nbsp;nm wide × 4&nbsp;μm tall.<ref>{{cite journal
 | last =Bach
 | first =Roger
 | title =Controlled double-slit electron diffraction
 | journal =New Journal of Physics
 | volume =15
 | issue =3
 |page=033018
 | date =March 2013
 | doi =10.1088/1367-2630/15/3/033018
|arxiv = 1210.6243 |bibcode = 2013NJPh...15c3018B | s2cid =832961
 |display-authors=etal}}</ref>

In 2013, a quantum interference experiment (using diffraction gratings, rather than two slits) was successfully performed with molecules that each comprised 810 atoms (whose total mass was over 10,000 [[atomic mass units]]).<ref name="medium.com">"[https://medium.com/the-physics-arxiv-blog/462c39db8e7b Physicists Smash Record For Wave–Particle Duality]"</ref><ref name="Eibenberger 2013 pp. 14696–14700">{{cite journal |last= Eibenberger |first=Sandra |title= Matter-wave interference with particles selected from a molecular library with masses exceeding 10000 amu |journal= [[Physical Chemistry Chemical Physics]] |volume=15 |issue=35 |pages= 14696–14700 |year= 2013 |doi= 10.1039/C3CP51500A |arxiv= 1310.8343 |bibcode = 2013PCCP...1514696E |display-authors=etal |pmid= 23900710|s2cid=3944699 }}</ref> The record was raised to 2000 atoms (25,000 amu) in 2019.<ref name="Yaakov Y. Fein 1242–1245"/>

====Hydrodynamic pilot wave analogs====

[[Hydrodynamic quantum analogs|Hydrodynamic analogs]] have been developed that can recreate various aspects of quantum mechanical systems, including single-particle interference through a double-slit.<ref name=Bush2015>{{cite journal|last1=Bush|first1=John WM|title=Pilot-wave hydrodynamics|journal=Annual Review of Fluid Mechanics|date=2015|volume=47|issue=1|pages=269–292|doi=10.1146/annurev-fluid-010814-014506|url=http://math.mit.edu/~bush/wordpress/wp-content/uploads/2015/01/Bush-AnnRev2015.pdf |archive-url=https://web.archive.org/web/20150621172430/http://math.mit.edu/~bush/wordpress/wp-content/uploads/2015/01/Bush-AnnRev2015.pdf |archive-date=2015-06-21 |url-status=live|access-date=21 June 2015|bibcode = 2015AnRFM..47..269B |hdl=1721.1/89790|hdl-access=free}}</ref> A silicone oil droplet, bouncing along the surface of a liquid, self-propels via resonant interactions with its own wave field. The droplet gently sloshes the liquid with every bounce. At the same time, ripples from past bounces affect its course. The droplet's interaction with its own ripples, which form what is known as a [[pilot wave]], causes it to exhibit behaviors previously thought to be peculiar to elementary particles – including behaviors customarily taken as evidence that elementary particles are spread through space like waves, without any specific location, until they are measured.<ref name=Bush2010>{{cite journal|last1=Bush|first1=John W. M.|title=Quantum mechanics writ large|journal=PNAS|volume=107|issue=41|pages=17455–17456|doi=10.1073/pnas.1012399107|bibcode = 2010PNAS..10717455B |pmc=2955131|year=2010|doi-access=free}}</ref><ref>{{Cite magazine |url=https://www.wired.com/2014/06/the-new-quantum-reality/ |title=Have We Been Interpreting Quantum Mechanics Wrong This Whole Time?|magazine=Wired |author=Natalie Wolchover |date=30 June 2014}}</ref>

Behaviors mimicked via this hydrodynamic pilot-wave system include quantum single particle diffraction,<ref name=CouderFort2012>{{cite journal|last1=Couder|first1=Y.|last2=Fort|first2=E.|title=Probabilities and trajectories in a classical wave–particle duality|journal=Journal of Physics: Conference Series|date=2012|volume=361|issue=1|page=012001|doi=10.1088/1742-6596/361/1/012001|bibcode = 2012JPhCS.361a2001C |doi-access=free}}</ref> tunneling, quantized orbits, orbital level splitting, spin, and multimodal statistics. It is also possible to infer uncertainty relations and exclusion principles.  Videos are available illustrating various features of this system. [[#External links|(See the External links.)]]

However, more complicated systems that involve two or more particles in superposition are not amenable to such a simple, classically intuitive explanation.<ref name="Baggott, Jim 2011 pp. 76">Baggott, Jim (2011). ''The Quantum Story: A History in 40 Moments''. New York: Oxford University Press. pp. 76.  ("The wavefunction of a system containing ''N'' particles depends on 3''N'' position coordinates and is a function in a 3''N''-dimensional configuration space or 'phase space'.  It is difficult to visualize a reality comprising imaginary functions in an abstract, multi-dimensional space.  No difficulty arises, however, if the imaginary functions are not to be given a real interpretation.")</ref> Accordingly, no hydrodynamic analog of entanglement has been developed.<ref name=Bush2015/> Nevertheless, optical analogs are possible.<ref>{{Cite journal | doi=10.1038/srep18574| pmid=26689679| pmc=4686973| title=Classical hypercorrelation and wave-optics analogy of quantum superdense coding| journal=Scientific Reports| volume=5| page=18574| year=2016| last1=Li| first1=Pengyun| last2=Sun| first2=Yifan| last3=Yang| first3=Zhenwei| last4=Song| first4=Xinbing| last5=Zhang| first5=Xiangdong| bibcode=2015NatSR...518574L}}</ref>

==== Double-slit experiment on time ====
In 2023, an experiment was reported recreating an interference pattern in time by shining a [[pump laser]] pulse at a screen coated in [[Indium tin oxide|indium tin oxide (ITO)]] which would alter the properties of the electrons within the material due to the [[Kerr effect]], changing it from transparent to reflective for around 200 femtoseconds long where a subsequent probe laser beam hitting the ITO screen would then see this temporary change in optical properties as a slit in time and two of them as a double slit with a phase difference adding up destructively or constructively on each frequency component resulting in an interference pattern.<ref name=":0">{{Cite journal |last1=Bacot |first1=Vincent |last2=Labousse |first2=Matthieu |last3=Eddi |first3=Antonin |last4=Fink |first4=Mathias |last5=Fort |first5=Emmanuel |date=November 2016 |title=Time reversal and holography with spacetime transformations |url=https://www.nature.com/articles/nphys3810 |journal=Nature Physics |language=en |volume=12 |issue=10 |pages=972–977 |doi=10.1038/nphys3810 |arxiv=1510.01277 |bibcode=2016NatPh..12..972B |s2cid=53536274 |issn=1745-2481}}</ref><ref>{{Cite journal |last=Rodríguez-Fortuño |first=Francisco J. |date=2023-04-03 |title=An optical double-slit experiment in time |url=https://www.nature.com/articles/s41567-023-02026-2 |journal=Nature Physics |volume=19 |issue=7 |language=en |pages=929–930 |doi=10.1038/s41567-023-02026-2 |bibcode=2023NatPh..19..929R |s2cid=257945438 |issn=1745-2481}}</ref><ref name=":1">{{Cite journal |last=Castelvecchi |first=Davide |date=2023-04-03 |title=Light waves squeezed through 'slits in time' |url=https://www.nature.com/articles/d41586-023-00968-4 |journal=Nature |language=en |volume=616 |issue=7956 |page=230 |doi=10.1038/d41586-023-00968-4|pmid=37012471 |bibcode=2023Natur.616..230C |s2cid=257922697 }}</ref> Similar results have been obtained classically on water waves.<ref name=":0" /><ref name=":1" />