Wave-Function Collapse as a Dynamical Process  

In General > s.a. wave-function collapse [including some models]; zeno effect.
* Idea: The point of view according to which wave-function collapse (quantum-state reduction) is a physical process, as opposed to just being related to our knowledge and description of the system; In a relativistic scenario the collapse will then happen at a finite speed, as opposed to the instantaneous collapse of the conventional view.
* Tests: One way to test it is to look for quantum behaviour in larger and larger objects; If collapse models are correct, then quantum effects will not be apparent above a certain mass; 2015, Physicists have already carried out double-slit interference experiments with large molecules; Various groups are planning to search for such a cut-off using metal clusters and nanoparticles, and hope to see results within a decade.
* Motivation: Using this point of view it becomes easier to explain how quantum fluctuations in the early universe might have become classical.
@ General references: Lewin FP(09) [as an effect of field quantization]; Omnčs a1006, a1601 [derivation of collapse from quantum dynamics].
@ Speed / time for collapse: Squires PLA(90); Pegg PLA(91); Zurek qp/03 ["decoherence timescale"]; Ohanian a1311 [atom-interferometer test].
@ State recovery / uncollapse: Katz et al PRL(08)-a0806; Jordan & Korotkov CP(10)-a0906 [undoing quantum measurements]; news PhysOrg(13)nov.
@ Objective collapse, and retina / mind: Georgiev qp/02; Thaheld qp/06/PRA, BioSys(08)qp/06; Ghirardi & Romano JPCS-a1401 [collapse models and perceptual processes]; Ghirardi IJTP(15)-a1411 [reply to Elio Conte].
@ Constraints: Jones et al FP(04)qp [SNO experiment]; Curceanu et al JAP(15)-a1502 [from X-ray experiments]; Helou et al PRD(17)-a1606, Carlesso et al PRD(16)-a1606 [from gravitational-wave detectors].
@ Other phenomenology: Squires PLA(91), Pearle et al FP(99)qp/00 [and radiation]; Pearle FP(12)-a1003 [and cosmogenesis]; Donadi et al FP(13)-a1207 [and neutrino oscillations], FP(13)-a1207 [and flavor oscillations]; Okon & Sudarsky FP(14)-a1309 [advantages for cosmology and quantum gravity]; Donadi & Bassi JPA(15)-a1408 [and electromagnetic radiation]; Toroš & Bassi a1601 [and matter-wave interferometry]; Simonov & Hiesmayr a1606 [and neutral meson flavor oscillations].
@ Collapse over a finite time: Marchewka & Schuss a1103; Ignatiev JPCS(13)-a1204.
@ Related topics: Bassi et al JPA(05)qp [and E non-conservation], JPA(07) [and Hilbert space operator formalism]; Bondoni a1006-wd [measurement as mathematical vs phenomenological.process]; Tumulka a1102 [paradoxes and primitive ontology]; Brouzakis et al PLB(12)-a1109; Weinberg PRA(12)-a1109; Rizos & Tetradis JHEP(12)-a1112; Simpson FP(11); Melkikh a1311 [and quantum field theory]; McQueen SHPMP(15)-a1501 [four tails problems]; Yun a1606 [entangling-speed threshold]; Bedingham & Maroney PRA(17)-a1607 [and time-reversal symmetry].

And Gravity > s.a. models of decoherence [gravity-related].
* History: In the first lecture of his 1962 course on gravitation Feynman speculated that gravity would enforce classical behavior for masses larger than the Planck mass; The idea is related to work on the quantum-classical divide and attempts at building and experimenting with hybrid quantum-classical devices.
* Gravity produces wave function collapse: A wave function collapses under the influence of gravity in a region where the matter density reaches a certain value (masses and lengths of the order of bacterial scales); Gravity provides a decoherence mechanism; Penrose's proposal is motivated by a fundamental conflict between the superposition principle of quantum mechanics and the principle of general covariance.
* Wave function collapse produces gravity: 2017, An idea proposed by Antoine Tilloy is that when a GRW-type flash collapses a wave function and causes a particle to be localized in one place, it creates a gravitational field at that event; Gravity remains classical.
@ General references: Károlyházy NC(66); Diósi PLA(84)-a1412; Károlyházy in(85), et al in(86); Diósi PRA(89); Ellis et al PLB(89); Fivel qp/97; Anandan FP(99)gq/98; Christian gq/98-ch; De Filippo qp/00, qp/01; De Filippo et al PhyA(03)qp [simulation]; Mureika PRD(06) [and large extra dimensions]; Adler JPA(07)qp/06; Salart et al PRL(08)-a0803 [and Bell inequalities]; Diósi JPCS(09)-a0902 [collapse causes gravity]; Diósi JPCS(13)-a1302; Sharma & Singh GRG(14)-a1403 [Ricci identities and Dirac equations]; Diósi FP(14), NJP(14)-a1404 [in bulk matter]; Singh JPCS-a1503 [survey]; Banerjee et al IJMPD(15)-a1505-GRF [and the cosmological constant and time].
@ Relativistic models: Quandt-Wiese a0912; Stoica Quanta(16)-a1601 [continuous evolution]; Quandt-Wiese a1701 , a1701 [from semiclassical gravity, wave function evolution in a dynamically expanding spacetime]; Gasbarri et al a1701 [mechanism]; Okon & Sudarsky a1701 [in cosmology and quantum gravity].
@ Other models: Melko & Mann gq/00 [D-dimensional Schrödinger-Newton equations]; Gao IJTP(10)-a1001 [and spacetime discreteness]; Adler a1401-ch [state vector reduction as driven by spacetime foam]; Bera et al a1608 [stochastic modification of the Schrödinger-Newton equation]; Brody & Hughston a1611 [energy-driven stochastic master equation for the density matrix]; Korbicz & Tuziemski a1612; Tilloy a1709 [GRW with massive flashes].
@ Penrose's proposal: Penrose in(81), in(86); Penrose GRG(96); Penrose in(00); Gao SHPMP(13)-a1305 [critique]; Oosterkamp & Zaanen a1401-conf [thought experiment]; Penrose FP(14); Bahrami et al PRA(14)-a1408 [cutoff, and dissipative generalization].
@ Gravitational self-interaction: Colin et al CQG(14)-a1403 [approximate dynamics and experimental setting].
@ Tests: Christian PRL(05)qp [with cosmic neutrinos]; van Wezel et al PhilM(08)-a0706 [towards an experimental test]; Quandt-Wiese a1701 [proposal].
> Phenomenology: see matter phenomenology in quantum gravity; models of dark energy; quantum cosmological perturbations.

Continuous Spontaneous Localization
* Idea: Models of spontaneous wave function collapse modify the linear Schrödinger equation by adding stochastic non-linear terms to it, which leads to non-conservation of energy for the system under consideration; The larger a system is, the faster a state superposition will collpase; > s.a. schrödinger equation.
* GRW mechanism: Gives a quantum theory without observers; In fact, two different ones by using either the matter density ontology (GRWm) or the flash ontology (GRWf); Testable deviations from quantum mechanics are known for both theories, but the difference is so small that no decisive experiment has been performed (2007).
@ General references: Pearle IJTP(79), PRA(89) [randomly fluctuating interaction]; Pearle & Soucek FPL(89) [path integral]; Ghirardi & Pearle in(90); Nicrosini & Rimini FP(90) [stochastic processes in \(\cal H\)]; Squires PLA(91) [without stochastic field]; Pearle in(97)qp/98, in(97)qp/98, LNP(99)qp, PRA(99)qp, FP(00)qp [and conservation laws], PRA(04)qp/03 [energy-driven]; Santos & Escobar qp/98 [beable interpretation]; Hansson qp/00 [from non-abelian non-linearity]; Bassi & Ghirardi PRP(03)qp; Bassi JPA(05)qp/04 [single free particle]; Dowker & Herbauts FPL(05)qp/04 [without wave function]; Pearle PRA(05)qp [quasirelativistic quasilocal model]; Lewis SHPMP(05) [interpretation]; Morikawa & Nakamichi PTP(06)qp/05 [as spontaneous symmetry breaking]; Pearle JPA(07)qp/06, qp/06 [overview]; Bassi JPCS(07)qp [rev]; Bassi et al RMP(13)-a1204 [rev, and tests], a1212/RMP [stochastic methods]; Bassi & Ulbricht JPCS(14)-a1401 [rev].
@ GRW mechanism: Ghirardi et al PRA(90); Tessieri et al PRA(95); Clifton & Monton BJPS(99), Bassi & Ghirardi BJPS(99), BJPS(99) [and enumeration principle]; Monton SHPMP(04) [interpretation]; Allori et al BJPS(08)qp/06 [and pilot-wave theory]; Vacchini JPA(07) [GRW master equation and decoherence]; Frigg & Hoefer SHPMP(07) [and probabilities]; Goldstein et al JSP(12)-a0710 [testable predictions]; Tumulka RVMP(09)-a0711 [flash ontology]; Bedingham JPA(11) [hidden-variable interpretation]; Esfeld & Gisin a1310 [John Bell's GRW flash theory]; Wallace a1407 [tails of the GRW wave function].
@ GRW mechanism, variations: Smirne et al PRA(14)-a1408 [dissipative extension]; Egg & Esfeld a1410 [GRW matter density theory (GRWm)].
@ For quantum field theory: Tumulka PRS(06)qp/05 [GRW]; Diósi AIP(06)qp [QED]; Derakhshani PLA(13)-a1304 [Newtonian theory of semiclassical gravity]; Pearle a1404-wd, PRD(15)-a1412 [scalar field, relativistic model]; Pearle a1610-in [for photons].
@ Phenomenology: Nimmrichter et al PRA(11) [tests with matter-wave interferometry]; Lochan et al PRD(12) [constraints from cmb spectral distortions]; Das et al a1302-MG13 [cosmology]; Laloë et al PRA(14)-a1409 [trapped ultra-cold atoms]; Diósi PRL(15)-a1411 [classical mechanical oscillators]; > s.a. black-hole information.

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