Editing Wave–particle duality (section)

== Electrons behaving as waves and particles ==
{{See also|Double-slit experiment}}
The electron double slit experiment is a textbook demonstration of wave-particle duality.<ref name=FeynmanIII/> A modern version of the experiment is shown schematically in the figure below.

[[File:Roger Bach et al 2013 New J. Phys. 15 033018 Nj458349f1.jpg|Left half: schematic setup for electron double-slit experiment with masking; inset micrographs of slits and mask; Right half: results for slit 1, slit 2 and both slits open.<ref name="Bach Pope Liou Batelaan 2013 p=033018"/>|center|thumb|554x554px]]

Electrons from the source hit a wall with two thin slits. A mask behind the slits can expose either one or open to expose both slits. The results for high electron intensity are shown on the right, first for each slit individually, then with both slits open. With either slit open there is a smooth intensity variation due to diffraction. When both slits are open the intensity oscillates, characteristic of wave interference.

Having observed wave behavior, now change the experiment, lowering the intensity of the electron source until only one or two are detected per second, appearing as individual particles, dots in the video. As shown in the movie clip below, the dots on the detector seem at first to be random. After some time a pattern emerges, eventually forming an alternating sequence of light and dark bands.

{{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 build up dot by dot. '''Click on the thumbnail to enlarge the movie.'''
}}

The experiment shows wave interference revealed a single particle at a time—quantum mechanical electrons display both wave and particle behavior. Similar results have been shown for atoms and even large molecules.<ref>{{Cite journal |last1=Arndt |first1=Markus |last2=Hornberger |first2=Klaus |date=2014 |title=Testing the limits of quantum mechanical superpositions |url=https://www.nature.com/articles/nphys2863 |journal=Nature Physics |language=en |volume=10 |issue=4 |pages=271–277 |arxiv=1410.0270v1 |doi=10.1038/nphys2863 |bibcode=2014NatPh..10..271A |s2cid=56438353 |issn=1745-2473}}</ref>