Physics:Quantum entanglement - Revision history

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	=References=		=References=
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	~~{{Quantum mechanics topics}}~~
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 == See also ==
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 == Further reading ==

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	'''entanglement''' ~~is a Book I topic in the Quantum Collection. Quantum~~ entanglement is the phenomenon wherein the quantum state of each particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical physics and quantum physics: entanglement is a primary feature of quantum mechanics not present in classical mechanics. process can split photons into type II photon pairs with mutually perpendicular polarization.]] Quantum entanglement is the phenomenon wherein the quantum state of each particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance.		'''entanglement''' quantum entanglement is the phenomenon wherein the quantum state of each particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical physics and quantum physics: entanglement is a primary feature of quantum mechanics not present in classical mechanics. process can split photons into type II photon pairs with mutually perpendicular polarization.]] Quantum entanglement is the phenomenon wherein the quantum state of each particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance. Measurements of physical properties such as position, momentum, spin, and polarization performed on entangled particles can, in some cases, be found to be perfectly correlated.
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	=== Paradox ===		=== Paradox ===
	~~{{main\|Physics~~:EPR paradox}}		''Related topic:'' EPR paradox

	The singlet state described above is the basis for one version of the EPR paradox. In this variant, introduced by David Bohm, a source emits particles and sends them in opposite directions. The state describing each pair is entangled.<ref>{{cite book\|first=David \|last=Bohm \|title=Quantum Theory \|orig-date=1951 \|year=1989 \|publisher=Dover \|edition=reprint \|isbn=0-486-65969-0 \|pages=611–622}}</ref> In the standard textbook presentation of quantum mechanics, performing a spin measurement on one of the particles causes the wave function for the whole pair to collapse into a state in which each particle has a definite spin (either up or down) along the axis of measurement. The outcome is random, with each possibility having a probability of 50%. However, if both spins are measured along the same axis, they are found to be anti-correlated. This means that the random outcome of the measurement made on one particle seems to have been transmitted to the other, so that it can make the "right choice" when it too is measured.<ref name="Zwiebach2022"/>{{rp\|§18.8}}<ref name="Griffiths">{{cite book\|first1=David J. \|last1=Griffiths \|author-link1=David J. Griffiths \|first2=Darrell F. \|last2=Schroeter \|title=Introduction to Quantum Mechanics \|title-link=Introduction to Quantum Mechanics (book) \|edition=3rd \|year=2018 \|publisher=Cambridge University Press \|isbn=978-1-107-18963-8 }}</ref>{{rp\|447–448}}		The singlet state described above is the basis for one version of the EPR paradox. In this variant, introduced by David Bohm, a source emits particles and sends them in opposite directions. The state describing each pair is entangled.<ref>{{cite book\|first=David \|last=Bohm \|title=Quantum Theory \|orig-date=1951 \|year=1989 \|publisher=Dover \|edition=reprint \|isbn=0-486-65969-0 \|pages=611–622}}</ref> In the standard textbook presentation of quantum mechanics, performing a spin measurement on one of the particles causes the wave function for the whole pair to collapse into a state in which each particle has a definite spin (either up or down) along the axis of measurement. The outcome is random, with each possibility having a probability of 50%. However, if both spins are measured along the same axis, they are found to be anti-correlated. This means that the random outcome of the measurement made on one particle seems to have been transmitted to the other, so that it can make the "right choice" when it too is measured.<ref name="Zwiebach2022"/>{{rp\|§18.8}}<ref name="Griffiths">{{cite book\|first1=David J. \|last1=Griffiths \|author-link1=David J. Griffiths \|first2=Darrell F. \|last2=Schroeter \|title=Introduction to Quantum Mechanics \|title-link=Introduction to Quantum Mechanics (book) \|edition=3rd \|year=2018 \|publisher=Cambridge University Press \|isbn=978-1-107-18963-8 }}</ref>{{rp\|447–448}}
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	===Multipartite entanglement===		===Multipartite entanglement===
	~~{{main\|~~Multipartite entanglement}}		''Related topic:'' Multipartite entanglement

	Quantum states describing systems made of more than two pieces can also be entangled. An example for a three-qubit system is the Greenberger–Horne–Zeilinger (GHZ) state,		Quantum states describing systems made of more than two pieces can also be entangled. An example for a three-qubit system is the Greenberger–Horne–Zeilinger (GHZ) state,
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	== Experiments demonstrating and using entanglement ==		== Experiments demonstrating and using entanglement ==
	===Bell tests===		===Bell tests===
	~~{{main\|Physics~~:Bell test}}		''Related topic:'' Bell test

	A Bell test, also known as ''Bell inequality test'' or ''Bell experiment'', is a real-world physics experiment designed to test the theory of quantum mechanics against the hypothesis of local hidden variables. These tests empirically evaluate the implications of Bell's inequality. To date, all Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems behave. Many types of Bell tests have been performed in physics laboratories, often with the goal of ameliorating problems of experimental design or set-up that could in principle affect the validity of the findings of earlier Bell tests. This is known as "closing loopholes in Bell tests". In earlier tests, it could not be ruled out that the result at one point could have been subtly transmitted to the remote point, affecting the outcome at the second location;<ref name=":2">{{cite web \|last=Francis \|first=Matthew \|date=30 October 2012 \|title=Quantum entanglement shows that reality can't be local \|url=https://arstechnica.com/science/2012/10/quantum-entanglement-shows-that-reality-cant-be-local/ \|access-date=22 August 2023 \|website=Ars Technica \|language=en-us}}</ref> however, "loophole-free" Bell tests have since been performed where the locations were sufficiently separated that communications at the speed of light would have taken longer—in one case, 10,000 times longer—than the interval between the measurements.<ref name=":1">{{cite journal \|last1=Matson \|first1=John \|title=Quantum teleportation achieved over record distances \|journal=Nature News \|date=13 August 2012 \|doi=10.1038/nature.2012.11163 \|s2cid=124852641}}</ref><ref name=":0">		A Bell test, also known as ''Bell inequality test'' or ''Bell experiment'', is a real-world physics experiment designed to test the theory of quantum mechanics against the hypothesis of local hidden variables. These tests empirically evaluate the implications of Bell's inequality. To date, all Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems behave. Many types of Bell tests have been performed in physics laboratories, often with the goal of ameliorating problems of experimental design or set-up that could in principle affect the validity of the findings of earlier Bell tests. This is known as "closing loopholes in Bell tests". In earlier tests, it could not be ruled out that the result at one point could have been subtly transmitted to the remote point, affecting the outcome at the second location;<ref name=":2">{{cite web \|last=Francis \|first=Matthew \|date=30 October 2012 \|title=Quantum entanglement shows that reality can't be local \|url=https://arstechnica.com/science/2012/10/quantum-entanglement-shows-that-reality-cant-be-local/ \|access-date=22 August 2023 \|website=Ars Technica \|language=en-us}}</ref> however, "loophole-free" Bell tests have since been performed where the locations were sufficiently separated that communications at the speed of light would have taken longer—in one case, 10,000 times longer—than the interval between the measurements.<ref name=":1">{{cite journal \|last1=Matson \|first1=John \|title=Quantum teleportation achieved over record distances \|journal=Nature News \|date=13 August 2012 \|doi=10.1038/nature.2012.11163 \|s2cid=124852641}}</ref><ref name=":0">

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	=== Entanglement of quarks and gluons in protons ===		=== Entanglement of quarks and gluons in protons ===
	Physicists at Brookhaven National Laboratory demonstrated quantum entanglement within protons, showing quarks and gluons are interdependent rather than isolated particles.<ref>{{cite web \|url=https://physicsworld.com/a/entanglement-entropy-in-protons-affects-high-energy-collisions-calculations-reveal/ \|title=Entanglement entropy in protons affects high-energy collisions, calculations reveal \|publisher=Physics World \|date=7 January 2025 }}</ref> Using high-energy electron-proton collisions, they revealed maximal entanglement, reshaping our understanding of proton structure.<ref>{{cite journal \|last=Hentschinski \|first=Martin \|display-authors=et al. \|year=2024 \|title=QCD evolution of entanglement entropy \|journal=IOP Publishing \|volume=87 \|issue=12 \|doi=10.1088/1361-6633/ad910b \|pmid=39527914 \|arxiv=2408.01259 \|bibcode=2024RPPh...87l0501H }}</ref>		Physicists at Brookhaven National Laboratory demonstrated quantum entanglement within protons, showing quarks and gluons are interdependent rather than isolated particles.<ref>{{cite web \|url=https://physicsworld.com/a/entanglement-entropy-in-protons-affects-high-energy-collisions-calculations-reveal/ \|title=Entanglement entropy in protons affects high-energy collisions, calculations reveal \|publisher=Physics World \|date=7 January 2025 }}</ref> Using high-energy electron-proton collisions, they revealed maximal entanglement, reshaping our understanding of proton structure.<ref>{{cite journal \|last=Hentschinski \|first=Martin \|display-authors=et al. \|year=2024 \|title=QCD evolution of entanglement entropy \|journal=IOP Publishing \|volume=87 \|issue=12 \|doi=10.1088/1361-6633/ad910b \|pmid=39527914 \|arxiv=2408.01259 \|bibcode=2024RPPh...87l0501H }}</ref>

	~~== See also ==~~
	~~{{#invoke:PhysicsQC\|tocHeadingAndList\|Physics:Quantum basics/See also}}~~

	== Further reading ==		== Further reading ==

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