Editing Double-slit experiment (section)

===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>