|  Entanglement of Quantum States | 
In General
  > s.a. Coherence; correlations;
  quantum experiments and foundations;
  types of quantum states [separable].
  * Idea: One of various quantities
    used to characterize non-local, stronger-than-classical correlations in quantum
    systems, even when isolated from one another; Two subsystems are entangled if
    the total wave function is not factorizable, which means that values cannot be
    assigned to a complete set of observables for each individual system; It is the
    "spooky action at a distance" that disturbed Einstein so much.
  * History: 1935, Concept of
    "Verschränkung" introduced by E Schrödinger when physicists
    were debating the EPR paradox; 2000, Long the subject of discussion by philosophers
    of quantum theory, it has recently come to play an essential role for physicists
    in their development of quantum information theory; Entangled state of 4 particles,
    and between Be atoms achieved; 2001, Entangled state of two trillion-atom gas
    clouds achieved; 2003, Two solid-state superconducting qubits entangled over
    0.7 mm (earlier only micron scale); 2003, Effects seen in the bulk properties
    of a magnetic salt crystal [@ news
    pw(03)sep];
    2004, 3- and 4-photon entanglement produced, beating the diffraction limit [@ news
    pw(04)may];
    2005, Entangled states of 6 Be atoms and 8 Ca atoms [@ news
    pw(05)dec];
    2007, A notion of generalized entanglement has emerged, defined through
    expectation values of preferred observables, without reference to a
    subsystem decomposition; 2007, entanglement sudden death observed [@ news
    pw(07)may];
    > s.a. history of quantum theory.
  * Uses: It allows teleportation
    and quantum key distribution, which are impossible in the classical world;
    > s.a. entanglement phenomenology.
  * And non-locality: It is often
    assumed that the most non-local states are the maximally entangled ones; This
    is not the case.
  @ II:
    Kwiat & Hardy AJP(00)jan [quantum cakes];
    Aczel 02;
    Terhal et al PT(03)apr;
    Adesso a0706 ["social aspects"].
  @ Reviews, intros: Eckert et al in(03)qp/02;
    Eisert & Plenio IJQI(03)qp [continuous variables];
    4 · Horodecki RMP(09)qp/07;
    Bengtsson & Życzkowski 06;
    Silverman 08;
    Koh a0902;
    Albert & Galchen SA(09)mar;
    Kanmani a0907;
    Gabriel a1003-dipl;
    Orzel a1208/AJP [limits];
    Walter et al a1612,
    Bengtsson & Życzkowski a1612-ch [multipartite];
    in Chang & Ge 17;
    Schroeder AJP(17)nov-a1703 [pictorial examples];
    Alsina a1706-PhD;
    Paneru et al RPP(20)-a1911;
    Gudder a2005.
  @ General references:
    Corwin AJP(84)apr;
    Życzkowski PRA(99) [volume];
    Brukner et al qp/01;
    Viola et al qp/04-proc [for sets of observables];
    news sn(10)nov [loophole closed];
    Li et al AMP(10)-a1012;
    Masanes et al JMP-a1111 [in more general theories];
    Balachandran et al PRL(13)-a1205,
    PRD(13)-a1301 [algebraic approach, based on the GNS construction];
    Aerts & Sozzo LNCS(14)-a1304;
    Aerts & Sassoli de Bianchi conf(16)-a1502 [and the extended Bloch representation];
    de Ronde & Massri a1809 [logos categorical approach];
    Gudder a1904 [general theory];
    Cai et al a2006 [for any definition of subsystems].
  @ Conceptual: Esfeld SHPMP(04) [and metaphysics of relations];
    Shih a0706;
    Bokulich & Jaeger ed-10 [philosophy];
    Sudbery AIP(11)-a1103 [philosophical lessons];
    Hobson a1607 [meaning];
    de Ronde & Massri a1808,
    a1911
      [definition in non-collapse, no-small-particles interpretations].
  @ Monogamy: Terhal IBM(04)qp/03-conf;
    Lancien et al PRL(16)-a1604;
    Raju a1809 [and violation of locality in quantum gravity].
  @ And fluctuations: Song et al PRB(10)-a1002;
    Bhaumik a1411 [from inherent quantum fluctuations];
    Frérot & Roscilde PRB(15)-a1506.
  @ And correlations: Verstraete et al PRL(04)qp/03 [vs correlations];
    Vedral JMO(07)qp [from higher-dimensional classical correlations];
    Klobus et al EPJD(19)-a1808 [multipartite entanglement without multipartite correlations].
  @ And non-locality:
    Methot & Scarani QIC(07)qp/06;
    Barrett et al PRL(06)qp [maximally entangled states];
    Koashi et al a0709;
    Spengler et al JPA(11)-a0907 [in discrete systems];
    Giraud et al a0907-proc;
    Mazzola et al PRA(10)-a1003 [entanglement, mixedness and non-locality];
    Gillis FP(11)-a1007;
    Vallone et al PRA(14)-a1106 [non-locality and entanglement as opposite properties];
    Buscemi PRL(12)
    + Massar & Pironio Phy(12)may [all entangled quantum states are non-local];
    Kupczynski AIP(12)-a1205;
    Liang et al PRA(12);
    Schmid et al a2004;
    > s.a. XY Chain.
  @ And topology: Kauffman & Lomonaco NJP(02)qp;
    Sugita a0704-proc [topological links];
    Kauffman & Mehrotra a1611 [topological braiding].
  @ For general probabilistic theories: Holik et al a1202 [informational invariance];
    Aubrun et al a1910 [and state superposition];
    > s.a. indefinite causal relations.
   Specific aspects: see phenomenology
    and measures of entanglement; entanglement in field theory and
    spacetime; examples of systems.
 Specific aspects: see phenomenology
    and measures of entanglement; entanglement in field theory and
    spacetime; examples of systems.
Related Topics
  > s.a. hidden variables; phase transitions;
  quantum statistical mechanics [entanglement thermodynamics];
  wigner functions.
  * Interpretation: In topological
    theories entanglement of subsystems can be given an intuitive interpretation in
    terms of "strings" connecting them; More generally, the density matrix
    of a mixed state can be represented by cobordisms of topological spaces.
  @ Subsystem-independent: Barnum et al PRL(04)qp/03,
    Viola & Barnum qp/07-proc [based on observables].
  @ And non-classicality: Marek et al PRA(09)-a0705;
    Ivan et al PRA(13)-a1306;
    Vogel & Sperling PRA(14)-a1401 [unified treatment];
    Gholipour & Shahandeh PRA(16)-a1603
      [entangled states of arbitrarily high temperature and number of particles].
  @ Entanglement of formation: Li & Fei PRA(10)-a1010;
    de Oliveira et al PRA(14)-a1312 [monogamous].
  @ Entanglement and information:
    Cerf & Adami PhyD(98)qp/96 [and measurement];
    Plenio & Vedral CP(98)qp [rev];
    Eisert PhD(01)qp/06;
    Macchiavello PhyA(04);
    Ainsworth FP(07).
  @ Entanglement in time:
    Milz et al a2011 [multipartite];
    Marletto et al a2103
      [temporal teleportation and emergent dynamics];
    Castellani a2104 [entropy].
  @ Limits to entanglement: Gambini et al PLA(08)-a0708 [from use of realistic rods].
  @ Geometry, interpretation:
    Kuś & Życzkowski PRA(01);
    Bertlmann et al PRA(02)qp/01;
    Lévay JPA(04)qp/03;
    Kirkpatrick qp/04 [interpretation];
    Leinaas et al PRA(06)qp;
    Życzkowski & Bengtsson in(06)qp [intro];
    Basu & Bandyopadhyay IJGMP(07) [and geometric phase];
    Cavalcanti et al PRA(08)-a0709 [and geometry of the space of states];
    Sawicki et al CMP(11)-a1007 [symplectic geometry];
    Kiosses JPA(14)-a1403
      [entanglement as pure spinor geometry, Cartan equation and Dirac spinors];
    Boyer et al PRA(17)-a1608;
    Bej & Deb QIP(19)-a1805 [and geometry of the space of states];
    Melnikov et al JHEP(19)-a1809 [topological];
    > s.a. geometric phase.
  @ Classical analog: Spreeuw FP(98);
    Massar et al PRA(01)qp/00;
    Lakshminarayan qp/01;
    Collins & Popescu PRA(02)qp/01;
    Solomon & Ho proc(10)-a1104 [topological and quantum entanglement];
    Matzkin AIP(11)-a1110 [fate of entanglement for vanishing Planck constant];
    Bharath & Ravishankar PRA(14)-a1401 [classical simulation];
    Snoke a1406 [classical, macroscopic model];
    Aiello et al NJP(15)-a1409;
    Fu & Wu a1502 [effective simulation];
    D'Ariano et al PRA(20)-a1909.
  @ Other topics:
    Schlienz & Mahler PRA(95);
    Lo & Popescu qp/97;
    Peres PS(98)qp/97;
    Yu Shi AdP(00)qp/98 [Gedankenexperiments];
    D'Ariano et al PLA(00)qp [Bell measurements];
    Ghirardi et al JSP(02)qp/01;
    Hewitt-Horsman & Vedral PRA(07)qp/06 [in the Heisenberg picture];
    Naudts & Verhulst PRA(07) [ensemble-averaged];
    Arveson CMP(09) [almost-surely entangled states];
    de la Torre et al EJP(10)-a1002;
    Zanardi & Campos Venuti JSM(13)-a1205 [entanglement susceptibility];
    Yamazaki EPL(13)-a1304 [in theory space];
    Brandão & Cramer PRB(15)-a1409 [area law and specific heat];
    Kollas a1603-MSc [thermodynamical structure];
    Richens et al PRL(17)-a1705
    + news gm(17)aug [and emergent classicality];
    Liu et al JHEP(18)-a1807 [and state scrambling];
    > s.a. uncertainty.
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