Editing Double-slit experiment (section)

==Variations of the experiment==

===Interference from individual particles===
An important version of this experiment involves single particle detection. Illuminating the double-slit with a low intensity  results in single particles being detected as white dots on the screen. Remarkably, however, an interference pattern emerges when these particles are allowed to build up one by one (see the image below).
{{multiple image
| align             = center
| perrow            = 1
| total_width       = 320
| image_style       = border:none;
| image1            = Roger Bach et al 2013 New J. Phys. 15 033018 Figure 3 cropped to top frame.jpg
| alt1              = Electron diffraction pattern
| image2            = Electron_buildup_movie_from_"Controlled_double-slit_electron_diffraction"_Roger_Bach_et_al_2013_New_J._Phys._15_033018.gif
| alt2              = Dots slowly filling an interference pattern.
| caption2          = Experimental electron double slit diffraction pattern.<ref name="Bach Pope Liou Batelaan 2013 p=033018">{{cite journal | last1=Bach | first1=Roger | last2=Pope | first2=Damian | last3=Liou | first3=Sy-Hwang | last4=Batelaan | first4=Herman | title=Controlled double-slit electron diffraction | journal=New Journal of Physics | publisher=IOP Publishing | volume=15 | issue=3 | date=2013-03-13 | issn=1367-2630 | doi=10.1088/1367-2630/15/3/033018 | page=033018 | arxiv=1210.6243 | bibcode=2013NJPh...15c3018B | s2cid=832961 | url=https://iopscience.iop.org/article/10.1088/1367-2630/15/3/033018}}</ref> Across the middle of the image at the top, the intensity alternates from high to low, showing interference in the signal from the two slits. Bottom: movie of the pattern being built up dot-by-dot. '''Click on the thumbnail to enlarge the movie.'''
}}
This demonstrates the [[wave–particle duality]], which states that all matter exhibits both wave and particle properties: The particle is measured as a single pulse at a single position, while the modulus squared of the wave describes the [[Probability amplitude|probability]] of detecting the particle at a specific place on the screen giving a statistical interference pattern.<ref>{{cite book |title=The Fabric of the Cosmos: Space, Time, and the Texture of Reality |first1=Brian |last1=Greene |publisher= Random House LLC |year=2007 |isbn=978-0-307-42853-0 |page=90 |url=https://books.google.com/books?id=DNd2K6mxLpIC&pg=PA90}}</ref> This phenomenon has been shown to occur with photons,<ref name="Ananthaswamy">{{cite book
 | last1  = Ananthaswamy
 | first1 = Anil 
 | title  = Through Two Doors at Once: The Elegant Experiment That Captures the Enigma of Our Quantum Reality
 | publisher = Penguin
 | date   = 2018
 | page  = 63
 | isbn   = 978-1-101-98611-0
 }}</ref> electrons,<ref>{{cite journal |last1= Donati |first1= O | last2= Missiroli |first2= G F |last3= Pozzi |first3= G |year= 1973 |title= An Experiment on Electron Interference |journal= American Journal of Physics |volume= 41 |issue = 5| pages = 639–644 |doi= 10.1119/1.1987321 |bibcode= 1973AmJPh..41..639D }}</ref> atoms, and even some molecules: with [[buckminsterfullerene]] ({{chem|C|60}}) in 2001,<ref name="buckyballs" /><ref>[http://www.quantum.at/research/molecule-interferometry-foundations/wave-particle-duality-of-c60.html Wave Particle Duality of C60] {{webarchive |url= https://web.archive.org/web/20120331115055/http://www.quantum.at/research/molecule-interferometry-foundations/wave-particle-duality-of-c60.html |date= 31 March 2012 }}</ref><ref>{{cite journal |last1= Nairz | first1= Olaf |last2= Brezger |first2 = Björn |last3= Arndt |first3= Markus |first4= Anton |last4=Zeilinger |year= 2001 | title= Diffraction of Complex Molecules by Structures Made of Light |journal= Phys. Rev. Lett. |volume = 87 |issue= 16|page= 160401 | doi=10.1103/physrevlett.87.160401|arxiv = quant-ph/0110012 |bibcode = 2001PhRvL..87p0401N | pmid=11690188| s2cid= 21547361 }}</ref><ref>{{cite journal | last1 = Nairz | first1 = O | last2 = Arndt | first2 = M | last3 = Zeilinger | first3 = A | year = 2003 | title = Quantum interference experiments with large molecules | url = https://vcq.quantum.at/fileadmin/Publications/2003-17.pdf | journal = American Journal of Physics | volume = 71 | issue = 4 | pages = 319–325 | doi = 10.1119/1.1531580 | bibcode = 2003AmJPh..71..319N | access-date = 4 June 2015 | archive-url =https://web.archive.org/web/20150604203129/http://vcq.quantum.at/fileadmin/Publications/2003-17.pdf| archive-date = 4 June 2015 }}</ref> with 2 molecules of 430 atoms ({{chem|C|60|(C|12|F|25|)|10}} and {{chem|C|168|H|94|F|152|O|8|N|4|S|4}}) in 2011,<ref>{{cite journal|display-authors=etal |last1=Stefan Gerlich |title=Quantum interference of large organic molecules |journal=Nature Communications |date=5 April 2011 |volume=2 |page=263 |doi=10.1038/ncomms1263 |pmid=21468015 |pmc=3104521 |bibcode=2011NatCo...2..263G }}</ref> and with molecules of up to 2000 atoms in 2019.<ref>{{cite journal |last1=Yaakov Fein |display-authors=etal|title=Quantum superposition of molecules beyond 25kDa |journal=Nature Physics |date=Dec 2019 |volume=15|issue=12|pages=1242–1245|doi=10.1038/s41567-019-0663-9 |bibcode=2019NatPh..15.1242F|s2cid=203638258|url=https://www.nature.com/articles/s41567-019-0663-9.epdf}}</ref>
In addition to interference patterns built up from single particles, up to 4 [[Quantum entanglement|entangled]] photons can also show interference patterns.<ref>Hessmo, B., M. W. Mitchell, and P. Walther. [https://cds.cern.ch/record/1733647/files/vol44-issue6-p011-e.pdf "Entangled photons show interference and bilocation."] CERN Courier (2004): 11.</ref>

{{anchor|Which way}}

===Mach-Zehnder interferometer===
{{Main|Mach–Zehnder interferometer}}
[[File:Mach–Zehnder interferometer.gif|thumb|Light in Mach–Zehnder interferometer produces interference (wave-like behavior) even when being detected one photon at a time (particle-like behavior)]]

The Mach–Zehnder interferometer can be seen as a simplified version of the double-slit experiment.<ref>{{Cite journal |last1=Maries |first1=Alexandru |last2=Sayer |first2=Ryan |last3=Singh |first3=Chandralekha |date=2020-07-01 |title=Can students apply the concept of "which-path" information learned in the context of Mach–Zehnder interferometer to the double-slit experiment? |url=https://pubs.aip.org/ajp/article/88/7/542/1044560/Can-students-apply-the-concept-of-which-path |journal=American Journal of Physics |language=en |volume=88 |issue=7 |pages=542–550 |doi=10.1119/10.0001357 |issn=0002-9505|arxiv=2005.07560 |bibcode=2020AmJPh..88..542M }}</ref> Instead of propagating through free space after the two slits, and hitting any position in an extended screen, in the interferometer the photons can only propagate via two paths, and hit two discrete photodetectors. This makes it possible to describe it via simple linear algebra in dimension 2, rather than differential equations.

A photon emitted by the laser hits the first beam splitter and is then in a superposition between the two possible paths. In the second beam splitter these paths interfere, causing the photon to hit the photodetector on the right with probability one, and the photodetector on the bottom with probability zero.<ref>{{Cite journal |last1=Marshman |first1=Emily |last2=Singh |first2=Chandralekha |date=2016-03-01 |title=Interactive tutorial to improve student understanding of single photon experiments involving a Mach–Zehnder interferometer |url=https://iopscience.iop.org/article/10.1088/0143-0807/37/2/024001 |journal=European Journal of Physics |volume=37 |issue=2 |pages=024001 |doi=10.1088/0143-0807/37/2/024001 |issn=0143-0807|arxiv=1602.06162 |bibcode=2016EJPh...37b4001M }}</ref> Blocking one of the paths, or equivalently detecting the presence of a photon on a path eliminates interference between the paths: both photodetectors will be hit with probability 1/2. This indicates that after the first beam splitter the photon does not take one path or another, but rather exists in a quantum superposition of the two paths.<ref name="vedral">{{cite book |first=Vlatko |last=Vedral |title=Introduction to Quantum Information Science |date=2006 |publisher=Oxford University Press |isbn=978-0-19-921570-6 |oclc=442351498 |author-link=Vlatko Vedral}}</ref>

==="Which-way" experiments and the principle of complementarity===
A well-known [[thought experiment]] predicts that if particle detectors are positioned at the slits, showing through which slit a photon goes, the interference pattern will disappear.<ref name="Feynman" /> This which-way experiment illustrates the [[complementarity (physics)|complementarity]] principle that photons can behave as either particles or waves, but cannot be observed as both at the same time.<ref>{{cite web
  | last = Harrison
  | first = David
  | title = Complementarity and the Copenhagen Interpretation of Quantum Mechanics
  | work = UPSCALE
  | publisher = Dept. of Physics, U. of Toronto
  | year = 2002
  | url = http://www.upscale.utoronto.ca/GeneralInterest/Harrison/Complementarity/CompCopen.html
  | access-date = 21 June 2008}}</ref><ref>{{cite web
  | last = Cassidy
  | first = David
  | title = Quantum Mechanics 1925–1927: Triumph of the Copenhagen Interpretation
  | work = Werner Heisenberg
  | publisher = American Institute of Physics
  | year = 2008
  | url = http://www.aip.org/history/heisenberg/p09.htm
  | access-date = 21 June 2008
  | archive-date = 14 January 2016
  | archive-url = https://web.archive.org/web/20160114094044/https://www.aip.org/history/heisenberg/p09.htm
  }}</ref><ref>{{cite conference
  | first = María C.
  | last = Boscá Díaz-Pintado
  | title = Updating the wave–particle duality
  | book-title = 15th UK and European Meeting on the Foundations of Physics
  | date = 29–31 March 2007
  | location = Leeds, UK
  | url = http://philsci-archive.pitt.edu/archive/00003568/
  | access-date = 21 June 2008}}</ref>
Despite the importance of this thought experiment in the history of quantum mechanics (for example, see the discussion on [[Bohr–Einstein debates#Post-revolution: First stage|Einstein's version of this experiment]]), technically feasible realizations of this experiment were not proposed until the 1970s.<ref name=Bartell1980>{{Cite journal | last1 = Bartell | first1 = L. | title = Complementarity in the double-slit experiment: On simple realizable systems for observing intermediate particle-wave behavior | doi = 10.1103/PhysRevD.21.1698 | journal = Physical Review D | volume = 21 | issue = 6 |pages=1698–1699 | year = 1980 |bibcode = 1980PhRvD..21.1698B }}</ref> (Naive implementations of the textbook thought experiment are not possible because photons cannot be detected without absorbing the photon.) Currently, multiple experiments have been performed illustrating various aspects of complementarity.<ref name="Zeilinger1999">{{Cite journal |last1=Zeilinger |first1=A. |author-link=Anton Zeilinger |year=1999 |title=Experiment and the foundations of quantum physics |journal=Reviews of Modern Physics |volume=71 |issue=2 |pages=S288–S297 |bibcode=1999RvMPS..71..288Z |doi=10.1103/RevModPhys.71.S288}}</ref>

An experiment performed in 1987<ref name="Mittelstaedt">{{cite journal
  | author=P. Mittelstaedt
  |author2=A. Prieur |author3=R. Schieder
   | title=Unsharp particle-wave duality in a photon split-beam experiment
  | journal=Foundations of Physics
  | volume=17
  | issue=9
  | pages=891–903
  | year=1987
  | doi=10.1007/BF00734319
|bibcode = 1987FoPh...17..891M |s2cid=122856271 }}</ref><ref>D.M. Greenberger and A. Yasin, "Simultaneous wave and particle knowledge in a neutron interferometer", ''Physics Letters'' '''A 128''', 391–4 (1988).</ref> produced results that demonstrated that partial information could be obtained regarding which path a particle had taken without destroying the interference altogether. This "wave-particle trade-off" takes the form of an [[Wave–particle duality relation|inequality]] relating the visibility of the interference pattern and the distinguishability of the which-way paths.<ref>{{Cite journal |last=Sen |first=D. |date=2014 |title=The uncertainty relations in quantum mechanics |url=https://www.jstor.org/stable/24103129 |journal=Current Science |volume=107 |issue=2 |pages=203–218 |jstor=24103129 |issn=0011-3891 |quote="However, the 'wave-particle trade-off is now expressed in terms of an inequality, known as Englert-Greenberger duality or simply wave-particle duality relation". See also ref 24 in this work.}}</ref>

===Delayed choice and quantum eraser variations===
{{Main|Delayed-choice quantum eraser}}
[[File:Wheeler telescopes set-up.svg|alt=Wheeler's Delayed Choice Experiment|thumb|A diagram of Wheeler's delayed choice experiment, showing the principle of determining the path of the photon after it passes through the slit]]
[[Wheeler's delayed-choice experiment]]s demonstrate that extracting "which path" information after a particle passes through the slits can seem to retroactively alter its previous behavior at the slits.

[[Quantum eraser]] experiments demonstrate that wave behavior can be restored by erasing or otherwise making permanently unavailable the "which path" information.

A simple do-it-at-home illustration of the quantum eraser phenomenon was given in an article in ''Scientific American''.<ref name="Hillmer2007">{{cite magazine|last=Hillmer|first=R.|year=2007|title=A do-it-yourself quantum eraser|url=https://www.scientificamerican.com/slideshow/a-do-it-yourself-quantum-eraser/|magazine=Scientific American|volume=296|issue=5|pages=90–95|doi=10.1038/scientificamerican0507-90|author2-link=Paul Kwiat|author2=Kwiat, P.|access-date=11 January 2016|bibcode = 2007SciAm.296e..90H }}</ref> If one sets polarizers before each slit with their axes orthogonal to each other, the interference pattern will be eliminated. The polarizers can be considered as introducing which-path information to each beam. Introducing a third polarizer in front of the detector with an axis of 45° relative to the other polarizers "erases" this information, allowing the interference pattern to reappear. This can also be accounted for by considering the light to be a classical wave,<ref name=Hillmer2007 />{{rp|91}} and also when using circular polarizers and single photons.<ref name=Chiao1995 />{{rp|6}} Implementations of the polarizers using [[Quantum entanglement|entangled]] photon pairs have no classical explanation.<ref name=Chiao1995>{{cite journal |last=Chiao |first=R. Y. |author2=P. G. Kwiat |author3=Steinberg, A. M.  |title=Quantum non-locality in two-photon experiments at Berkeley|journal=Quantum and Semiclassical Optics: Journal of the European Optical Society Part B |year=1995 |volume=7 |issue=3 |pages=259–278  |doi=10.1088/1355-5111/7/3/006|arxiv = quant-ph/9501016 |bibcode = 1995QuSOp...7..259C |s2cid=118987962 }}</ref>

===Weak measurement===
{{Main|Weak measurement}}
In a highly publicized experiment in 2012, researchers claimed to have identified the path each particle had taken without any adverse effects at all on the interference pattern generated by the particles.<ref>{{cite web|last=Francis|first=Matthew|title=Disentangling the wave–particle duality in the double-slit experiment|url=https://arstechnica.com/science/2012/05/disentangling-the-wave-particle-duality-in-the-double-slit-experiment/|website=Ars Technica|date=21 May 2012}}</ref> In order to do this, they used a setup such that particles coming to the screen were not from a point-like source, but from a source with two intensity maxima. However, commentators such as Svensson<ref name=Svensson2013>{{cite journal|last=Svensson|first=Bengt E. Y.|title=Pedagogical Review of Quantum Measurement Theory with an Emphasis on Weak Measurements |journal=Quanta |volume=2 |issue=1 |pages=18–49 |doi=10.12743/quanta.v2i1.12 |year=2013|arxiv=1202.5148 |s2cid=119242577 }}</ref> have pointed out that there is in fact no conflict between the [[weak measurement]]s performed in this variant of the double-slit experiment and the [[Heisenberg uncertainty principle]]. Weak measurement followed by post-selection did not allow simultaneous position and momentum measurements for each individual particle, but rather allowed measurement of the average trajectory of the particles that arrived at different positions. In other words, the experimenters were creating a statistical map of the full trajectory landscape.<ref name=Svensson2013/>

===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" />