|  Classical Limit of Quantum Theory and Quantum-to-Classical Transition | 
Classical Limit
  > s.a. classical-quantum relationship; Correspondence
  Principle; macroscopic systems.
  * Idea: A limit in which quantum
    uncertainties of operators vanish; Usually identified with the \(\hbar\)/action
    → 0 limit, but in some situations there are other possibilities [@ Rajeev
    ht/02-proc];
    Possible settings for the limit are the following,
  - As a limit for the theory, in the
    sense of quantum mechanics as a deformation of classical mechanics;
  - As a sector for the theory containing
    states with classical behavior, like coherent or squeezed states;
  - As an approximation to the behavior of
    some states, such as the WKB approximation or limited measurement accuracy;
  - As a dynamical process that makes
    certain states acquire a more classical behavior, typically decoherence by
    interaction with the environment.
  * Remark: In terms of information,
    redundancy has been proposed as a prerequisite for objectivity, the defining
    property of classical objects.
  @ Books, intros: Maslov & Fedoriuk 81;
    Lazutkin 93;
    Brack & Bhaduri 97;
    Yam SA(97)jun; Landsman 98.
  @ The h → 0 limit: Man'ko & Man'ko JRLR(04)qp/04 [classical mechanics not limit of quantum mechanics];
    Castagnino & Gadella FP(06) [and self-induced decoherence];
    Kazandjian AJP(07)aug;
    Klein AJP(12)nov-a1201;
    Driver & Tong a1511.
Quantum-to-Classical Transition
  > s.a. cosmological perturbations; entanglement death;
  quantum field theory states; wave-function collapse.
  * Idea: The
    quantum-to-classical transition depends on several parameters, including
    an action scale \(\hbar\), a measure D of the coupling between
    a system and its environment, and, for chaotic systems, the Lyapunov
    exponent λ (the limit is achieved in a qualitatively
    different way for classically chaotic systems).
  * Interaction with the
    environment: The environment may not only induce classical
    properties like superselection rules, pointer states or even classical
    behavior of the quantum system, but also allow the transition from a
    statistical description of infinite quantum systems to the quantum
    mechanics of systems with a finite number of degrees of freedom.
  @ General references: Cini & Serva FPL(90) [intrinsic probabilities to classical statistics];
    Habib et al PRL(02) [and decoherence];
    Date CQG(07)gq/06 [constructing the classical theory];
    Hartle FP(11)-a0806;
    Wisniacki & Toscano PRE(09)-a0810 [scaling laws];
    Requardt a1009;
    Kofler & Brukner a1009
      [fundamental limits to quantum description];
    Oliveira et al a1101 [information accessibility];
    Paavola et al PRA(11)-a1103 [dependence of dynamical features on the measure for non-classicality used];
    Roemer a1112-conf;
    Hájíček JPCS(12)-a1201;
    Durt & Debierre IJMPB(13)-a1206 [entanglement-free regime and classical particles];
    Recchia & Teta JMP(14)-a1305
      [model for the emergence of a semiclassical state from interaction with the environment];
    Kak NQ-a1309 [condition on probabilities];
    Schlosshauer a1404-in [and decoherence, pedagogical];
    Raftery et al PRX(14) [dissipation-induced];
    Kak a1410
      [computability and insufficiency of unitary evolution];
    Briggs & Feagin a1506 [without decoherence];
    Rosaler a1511 [interpretation-neutral account];
    Kastner et al ed-17;
    Coecke et al EPTCS(18)-a1701 [two roads];
    Gozzi a1806 [without the zero-Planck-constant limit];
    Hollowood a1906 [from Born's rule].
  @ Measurement limitations: Kofler & Brukner PRL(07);
    Angelo a0809;
    Jeong et al PRL(14);
    Veeren & de Melo a2003
      [and entropic uncertainty relations].
  @ In pilot-wave quantum theory:
    Dürr & Römer JFA(10)-a1003 [classical limit for Hagedorn wave packets];
    Toroš et al JPA(16)-a1603 [collapse and classicality].
  @ Specific mechanisms, formalisms:
    Korbicz & Lewenstein FP(07) [group-theoretic formalism];
    Halliwell JPCS(09)-a0903 [via commuting X and P operators];
    Ellis & Rothman IJTP(10)-a0912 [Crystallizing Block Universe];
    Lochan et al GRG(15)-a1404 [spontaneous dynamical classicalization];
    Hollowood a1803
      [macroscopic systems coupled to their environments];
    Bhatt et al a1808 [GRW spontaneous localization];
    Bolaños EJP(18)-a1904 [phase space measurements];
    Coppo et al SC-a2004 [Yaffe's generalized coherent states approach].
  @ For specific systems: Fink et al PRL(03)-a1003 [for cavity QED];
    Toscano & Wisniacki PRE(06)qp [in kicked oscillator];
    Everitt et al PRA(09) [single field mode];
    Budiyono FP(10) [single particle];
    Pokharel et al a1604
      [driven double-well oscillator, dynamical complexity];
    Pan et al a1910 [in electron-photon interactions];
    > s.a. Caldeira-Leggett Model.
 Related pages: see relationship
  classical-quantum theory; semiclassical effects and degree
  of quantumness.
 Related pages: see relationship
  classical-quantum theory; semiclassical effects and degree
  of quantumness.
Semiclassical Theory and Approximation
  > s.a. foundations of quantum mechanics; quantum measurement.
  @ Semiclassical theory:
    Heller & Tomsovic PT(93)jul;
    Baranger et al JPA(01)qp [and coherent states];
    Pol'shin qp/02-wd [as phase space contraction];
    de Gosson JPA(02) [and symplectic camel];
    Castagnino PhyA(04)qp/05 [classical-statistical limit];
    dos Santos & de Aguiar BJP(05)qp/04 [and coherent state path integral ambiguity];
    Bracken & Wood PRA(06)qp/05 [semiclassical vs semiquantum];
    Struyve IJMPA(20)-a1507 [based on Bohmian mechanics];
    Vachaspati & Zahariade PRD(18)-a1806 [classical-quantum correspondence and backreaction, and toy model];
    Baytaş et al PRA(19)-a1811
      [as a canonical dynamical system that extends the classical phase space].
  @ Semiclassical approximation: Peres PS(86) [for Wigner function];
    De Alwis PLB(93)ht [2D dilaton gravity];
    Werner qp/95;
    Huang PRD(96) [conditions for consistency];
    de Gosson JPA(98) [with half-densities];
    Yoneda et al NCB(01) [continuous transition];
    Davis & Ghandour PLA(03) [and action-angle variables];
    Kowalski et al PLA(03) [and wavelet complexity];
    Ballentine PRA(04) [\(\hbar\)-dependence of averages];
    Vergini JPA(04) [chaotic eigenfunctions];
    Stuckey et al qp/06/FP [relational blockworld];
    Sen & Sengupta FPL(06) [unconventional view];
    Paul a0901 [long-time results];
    Yang PRD(17)-a1703 [loss of unitarity].
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