Editing Quantum decoherence (section)

===Origin of the concepts===
[[Nevill Mott]]'s solution to the iconic [[Mott problem]] in 1929 is considered in retrospect to be the first quantum decoherence work.<ref name=FigariTeta>{{Cite journal |last1=Figari |first1=Rodolfo |last2=Teta |first2=Alessandro |date=March 2013 |title=Emergence of classical trajectories in quantum systems: the cloud chamber problem in the analysis of Mott (1929) |url=http://link.springer.com/10.1007/s00407-012-0111-z |journal=Archive for History of Exact Sciences |language=en |volume=67 |issue=2 |pages=215–234 |doi=10.1007/s00407-012-0111-z |issn=0003-9519|arxiv=1209.2665 }}</ref> It was cited by the first modern theoretical treatment.<ref>{{Cite journal |last1=Joos |first1=E. |last2=Zeh |first2=H. D. |date=1985 |title=The emergence of classical properties through interaction with the environment |url=http://link.springer.com/10.1007/BF01725541 |journal=Zeitschrift für Physik B |language=en |volume=59 |issue=2 |pages=223–243 |doi=10.1007/BF01725541 |bibcode=1985ZPhyB..59..223J |issn=0722-3277}}</ref>

Although he did not use the term, the concept of quantum decoherence was first introduced in 1951 by the American physicist [[David Bohm]],<ref>{{Cite book |last=Bohm |first=David |title=Quantum Theory |publisher=[[Dover Publications]] |year=1951 |isbn=0-486-65969-0 |pages=600–609}}</ref><ref>{{cite journal |last1=Brown |first1=Harvey |last2=Wallace |first2=David |date=2005-04-01 |title=Solving the Measurement Problem: De Broglie-Bohm Loses Out to Everett |url=https://link.springer.com/article/10.1007/s10701-004-2009-3 |journal=Foundations of Physics |volume=35 |issue=4 |pages=517–540 |doi=10.1007/s10701-004-2009-3 |access-date=2024-02-26|arxiv=quant-ph/0403094 |bibcode=2005FoPh...35..517B }}</ref> who called it the "destruction of interference in the process of measurement". Bohm later used decoherence to handle the measurement process in the [[De Broglie–Bohm theory|de Broglie-Bohm interpretation]] of quantum theory.<ref>{{Cite journal |last=Bohm |first=David |date=1952-01-15 |title=A Suggested Interpretation of the Quantum Theory in Terms of "Hidden" Variables. II |url=https://link.aps.org/doi/10.1103/PhysRev.85.180 |journal=Physical Review |language=en |volume=85 |issue=2 |pages=180–193 |doi=10.1103/PhysRev.85.180 |bibcode=1952PhRv...85..180B |issn=0031-899X}}</ref>

The significance of decoherence was further highlighted in 1970 by the German physicist [[H. Dieter Zeh]],<ref name="Zeh" /> and it has been a subject of active research since the 1980s.<ref name="Schlosshauer">{{cite journal |last=Schlosshauer |first=Maximilian |year=2005 |title=Decoherence, the measurement problem, and interpretations of quantum mechanics |journal=[[Reviews of Modern Physics]] |volume=76 |issue=4 |pages=1267–1305 |doi=10.1103/RevModPhys.76.1267 |arxiv=quant-ph/0312059 |bibcode=2004RvMP...76.1267S |s2cid=7295619}}</ref> Decoherence has been developed into a complete framework, but there is controversy as to whether it solves the [[measurement problem]], as the founders of decoherence theory admit in their seminal papers.<ref name="Adler2001">{{cite journal |last=Adler |first=Stephen L. |year=2003 |title=Why decoherence has not solved the measurement problem: a response to P.W. Anderson |journal=[[Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics]] |volume=34 |issue=1 |pages=135–142 |arxiv=quant-ph/0112095 |doi=10.1016/S1355-2198(02)00086-2 |bibcode=2003SHPMP..34..135A |s2cid=21040195 |quote=Joos and Zeh (1985) state 'Of course no unitary treatment of the time dependence can explain why only one of these dynamically independent components is experienced'. And in a recent review on decoherence, Joos (1999) states ‘Does decoherence solve the measurement problem? Clearly not. What decoherence tells us is that certain objects appear classical when observed. But what is an observation? At some stage we still have to apply the usual probability rules of quantum theory'.}}</ref>

The study of decoherence as a proper subject began in 1970, with H. Dieter Zeh's paper "On the Interpretation of Measurement in Quantum Theory".<ref name="camilleri2009"/><ref name="Zeh">{{cite journal|first=H. Dieter |last=Zeh |title=On the Interpretation of Measurement in Quantum Theory |journal=Foundations of Physics |volume=1 |pages=69–76 |year=1970|issue=1 |doi=10.1007/BF00708656 |bibcode=1970FoPh....1...69Z |s2cid=963732 }}</ref> Zeh regarded the wavefunction as a physical entity, rather than a calculational device or a compendium of statistical information (as is typical for Copenhagen-type interpretations), and he proposed that it should evolve unitarily, in accord with the Schrödinger equation, at all times. Zeh was initially unaware of [[Hugh Everett III]]'s earlier work,<ref name=everett57>{{cite journal|first=Hugh |last=Everett |title=Relative State Formulation of Quantum Mechanics |journal=Reviews of Modern Physics |volume=29 |year=1957 |issue=3 |pages=454–462 |doi=10.1103/RevModPhys.29.454|bibcode=1957RvMP...29..454E }}</ref> which also proposed a universal wavefunction evolving unitarily; he revised his paper to reference Everett after learning of Everett's "relative-state interpretation" through an article by [[Bryce DeWitt]].<ref name="camilleri2009"/> (DeWitt was the one who termed Everett's proposal the [[many-worlds interpretation]], by which name it is commonly known.) For Zeh, the question of how to interpret quantum mechanics was of key importance, and an interpretation along the lines of Everett's was the most natural. Partly because of a general disinterest among physicists for interpretational questions, Zeh's work remained comparatively neglected until the early 1980s, when two papers by [[Wojciech Zurek]]<ref name="zurek81">{{cite journal|first=Wojciech H. |last=Zurek |title=Pointer Basis of Quantum Apparatus: Into what Mixture does the Wave Packet Collapse? |journal=Physical Review D |volume=24 |pages=1516–1525 |year=1981 |issue=6 |doi=10.1103/PhysRevD.24.1516|bibcode=1981PhRvD..24.1516Z }}</ref><ref name="zurek82">{{cite journal|first=Wojciech H. |last=Zurek |title=Environment-Induced Superselection Rules |journal=Physical Review D |volume=26 |pages=1862–1880 |year=1982 |issue=8 |doi=10.1103/PhysRevD.26.1862|bibcode=1982PhRvD..26.1862Z }}</ref> invigorated the subject. Unlike Zeh's publications, Zurek's articles were fairly agnostic about interpretation, focusing instead on specific problems of density-matrix dynamics. Zurek's interest in decoherence stemmed from furthering Bohr's analysis of the double-slit experiment in his reply to the [[Einstein–Podolsky–Rosen paradox]], work he had undertaken with [[Bill Wootters]],<ref>{{cite journal|first1=W. K. |last1=Wootters |first2=W. H. |last2=Zurek |title=Complementarity in the double-slit experiment: Quantum nonseparability and a quantitative statement of Bohr's principle |journal=Physical Review D |volume=19 |year=1979 |issue=2 |pages=473–484 |doi=10.1103/PhysRevD.19.473|bibcode=1979PhRvD..19..473W }}</ref> and he has since argued that decoherence brings a kind of rapprochement between Everettian and Copenhagen-type views.<ref name="camilleri2009"/><ref>{{cite book|chapter=Decoherence: From Interpretation to Experiment |first=M. |last=Schlosshauer |arxiv=2204.09755 |title=From Quantum to Classical |series=Fundamental Theories of Physics |year=2022 |volume=204 |publisher=Springer |doi=10.1007/978-3-030-88781-0_3 |isbn=978-3-030-88780-3 |editor-last=Kiefer |editor-first=C. |pages=45–64|s2cid=248299632 }}</ref>

Decoherence does not claim to provide a mechanism for some actual wave-function collapse; rather it puts forth a reasonable framework for the appearance of wave-function collapse. The quantum nature of the system is simply entangled into the environment so that a total superposition of the wave function still exists, but exists—at least for all practical purposes—beyond the realm of measurement.<ref>[[Roger Penrose]] (2004), ''[[The Road to Reality]]'', pp. 802–803: "...the environmental-decoherence viewpoint [...] maintains that state vector reduction [the R process] can be understood as coming about because the environmental system under consideration becomes inextricably entangled with its environment. [...] We think of the environment as extremely complicated and essentially 'random' [...], accordingly we sum over the unknown states in the environment to obtain a density matrix [...] Under normal circumstances, one must regard the density matrix as some kind of approximation to the whole quantum truth. For there is no general principle providing an absolute bar to extracting information from the environment. [...] Accordingly, such descriptions are referred to as FAPP [for all practical purposes]".</ref><ref>[[Huw Price]] (1996), ''Times' Arrow and Archimedes' Point'', p. 226: "There is a world of difference between saying 'the environment explains why collapse happens where it does' and saying 'the environment explains why collapse seems to happen even though it doesn't really happen'."</ref> By definition, the claim that a merged but unmeasurable wave function still exists cannot be proven experimentally. Decoherence is needed to understand why a quantum system begins to obey classical probability rules after interacting with its environment (due to the suppression of the interference terms when applying Born's probability rules to the system).

Criticism of the adequacy of decoherence theory to solve the measurement problem has been expressed by [[Anthony Leggett]].<ref>{{Cite journal |doi = 10.1238/Physica.Topical.102a00069|title = Probing quantum mechanics towards the everyday world: where do we stand|year = 2001|last1 = Leggett|first1 = A. J.|journal = Physica Scripta|volume = 102|issue = 1|pages =  69–73| s2cid=35691853 }}</ref><ref>{{Cite journal |doi = 10.1088/0953-8984/14/15/201|title = Testing the limits of quantum mechanics: Motivation, state of play, prospects|year = 2002|last1 = Leggett|first1 = A. J.|journal = Journal of Physics: Condensed Matter|volume = 14|issue = 15|pages = R415–R451| s2cid=250911999 }}</ref>