|  Random Walk | 
Random Walks in General 
  > s.a. diffusion; Semigroups.
  * Idea: A probability measure on
    the space of all paths on a space; Can be considered as a type of open system;
    For example, Brownian motion.
  * Specification: It can be
    assigned as a transition probability from each incomplete, n-step path,
    to each extension to n+1 steps; A simple type of situation is a Markov
    process, in which the probability only depends on the n-th configuration.
  * Displacement: In a space of Hausdorff
    dimension d, the mean square displacement after N steps is
    \(\langle\)D2\(\rangle\)
    ~ N 2/d; The planar
    (d = 2) self-avoiding walk has rms displacement exponent 3/4
    (long conjectured, proved in 2001).
  * Applications:
    Used to sample a space of states in randomized algorithms.
  @ General references: Feynman et al 63, I-6-6 (simple);
    Franceschetti et al AJP(93)dec [as eigenvalue problem];
    Hughes 95,
  96;
    in Ambjørn et al 97;
    Marchetti & da Silva BJP(99)mp/04 [and Brownian motion];
    Barkema et al PRL(01) [with random static traps];
    Campanino & Petritis in(04)m.PR/02 [survey and relevance];
    Nakamura & Small PLA(07) [test];
    Lawler & Limic 10;
    Rudnick & Gaspari 10 [advanced intro].
  @ Statistics: Ferraro & Zaninetti PhyA(04) [statistics of visits];
    Zhang et al CTP(11)-a1010 [1D, recurrence properties];
    Bénichou & Voituriez PRP(14) [evaluation of mean first-passage time].
  @ Related topics: Bellissard et al JPA(97) [distributions, using non-commutative geometry];
    Zia & Schmittmann AJP(03)sep [distribution of variances];
    Majumdar & Trizac PRL(19)
    + news pt(19)aug [application to integral calculations];
    > s.a. particle effects in quantum gravity.
Special Types
  > s.a. Lévy Process; dynamical triangulations.
  * Polya walk:
    The walker takes one step at integer numbers of time steps of the same width.
  * Montroll-Weiss continuous-time walk:
    The time intervals between successive steps are independent, exponentially and
    identically distributed random variables.
  * Self-avoiding:
    In 3D the expected length after N steps goes like N 0.6
    rather than N 0.5 as the simple random walk or diffusion.
  * Types of flights: Benoît Mandelbrot called Lévy
    flight, Cauchy flight and Rayleigh flight random walks with different step size probability distributions.
  @ Types of processes:
    Burda et al PRL(09)
      [maximal entropy random walk, localization];
    Cabezas et al JSP(14)-a1307 [activated, critical behavior];
    Bénichou et al PhyA(13)
      [inequivalence of the discrete-time Polya walk and the Montroll-Weiss continuous-time random walk];
    Garbaczewski & Żaba APPB(15)-a1412 [non-local];
    Sciarretta a1605 [simulating quantum mechanics].
  @ On random sets: Barat & Chakrabarti PRP(95);
    Faggionato et al CMP(06);
    Caputo & Faggionato AAP(07)m.PR/06;
    Zeitouni JPA(06) [rev];
    Bogachev in(06)-a0707 [rev];
    Juhász JPA(08) [renormalization group approach];
    Lenci a0810-wd [invariance principle and recurrence];
    > s.a. voronoi tilings.
  @ On other sets: Bender et al JMP(94) [non-integer dimension];
    Woess 00 [infinite graphs];
    Davison et al JPA(01) [fractals];
    Kostrykin & Schrader m.CO/04 [on graphs, generating functions];
    Franceschetti JSP(07) [inside n-disk];
    Mazzolo JPA(09) [bounded geometries];
    Telcs JSP(10) [Penrose lattice];
    Turban JPA(14) [fully connected lattice].
  @ Self-avoiding: Prellberg JPA(01) [scaling];
    Hueter m.PR/01 [D = 2],
    m.PR/01 [D > 2];
    Brydges et al ProbS(09)-a0906 [functional-integral representation];
    Clisby JSP(10)-a1005 [pivot algorithm];
    Guttmann APN-a1212 [rev].
Quantum Walk > s.a. classical limit;
  decoherence; quantum computation.
  * Rem: A quantum random walker
    is capable of moving much faster than its classical counterpart.
  @ Reviews: Kempe CP(03)qp;
    Venegas-Andraca QIP(12)-a1201 [comprehensive review].
  @ General references: Aharonov et al PRA(93) [introduction];
    Childs et al QIP(02)qp/01 [vs classical]; 
    Konno FNL(05)qp/04 [quantum to classical, path integral];
    Wang & Douglas qp/07-wd [applied to graph isomorphism problem];
    Yin et al PRA(08)-a0708 [in a random environment];
    Manouchehri & Wang PRA(09)-a0809 [physical realization];
    Chandrashekar PhD(09)-a1001;
    Sarkar et al Pra(17)-a1505 [effective Hamiltonian approach];
    Boettcher et al PRA(15)-a1410,
    Dadras et al a1802 [relation with classical random walk];
    Funakawa et al a1901 [time operators];
    Sako a2003 [categorical framework].
  @ Models, realizations: Dür et al PRA(02)qp [experiment proposal];
    Kosik CEJP(03) [two models];
    Schmitz et al PRL(09) [trapped ion];
    Krovi et al PRA(10) [spatial search with hitting time ∝
      tclassical1/2 using adiabatic quantum computing];
    Grünbaum & Velázquez a1111 [on the non-negative integers];
    Matsue et al a1507 [on simplicial complexes].
  @ Discrete time: 
    Molfetta & Debbasch JMP(12) [continuous limit];
    Joshi et al a1802 [path-integral approach];
    Arnault et al PRA(19)-a1807 [as lattice fermions];
    Chagas & Portugal EPTCS-a2001 [on oriented graphs];
    Vallejo et al a2004 [entropy production].
  @ Continuous time: Strauch PRA(06) [and discrete];
    Manouchehri & Wang JPA(07)qp/06 [state space must be discrete];
    Jafarizadeh & Sufiani a0704 [spectral analysis];
    Childs CMP(10)-a0810 [and discrete];
    Agliari et al JPA(08)-a0810;
    Salimi AP(09) [on star graphs];
    Mülken & Blumen PRP(11)
      [and coherent transport on complex networks];
    Falloon et al CPC(17)-a1606 [on arbitrary  graphs, QSWalk Mathematica package];
    Chia et al Quant(17)-a1608 [hitting time].
  @ Continuous, as limit of discrete: D'Alessandro RPMP(10)-a0902;
    Dheeraj & Brun PRA(15)-a1501;
    Arrighi et al a1505 [continuum limit as Dirac particle in curved spacetime];
    Arrighi & Facchini a1609 [arbitrary dimensions, curved spacetime];
    Arrighi et al a1711;
    Arrighi et al PRA(18)-a1803 [Dirac equation, honeycomb and triangular lattices];
    Di Molfetta & Arrighi a1906 [with a continuous-spacetime limit].
  @ 1D: Carteret et al JPA(03)qp [asymptotics];
    Romanelli et al PhyA(04)qp/03 [as Markov process];
    Fuss et al a0705 [analytic solution];
    Štefaňák et al NJP(09)-a0902 [biased, Polya number];
    Hinarejos et al a1204 [using Wigner functions];
    Dukes RiP(14)-a1405 [on circles, state revivals];
    > s.a. Wojcik Model.
  @ 2D: Watabe et al PRA(07)-a0802 [1-parameter family, limit distributions];
    Bressler et al a0903 [examples and phenomena];
    Baryshnikov et al JSP(10).
  @ Relativistic effects: Strauch JMP(07) [and Dirac equation];
    Kurzyński PLA(08) [Klein's paradox and Zitterbewegung].
  @ Related topics: Martin et al PRD(05)gq/04 [in generalized quantum mechanics];
    Rodríguez-Rosario et al PRA(10)-a0905 [quantum stochastic walk];
    Feng et al a1010 [of waves];
    Gudder & Sorkin GRG(11)-a1105 [two-site, quantum measure];
    Ellinas et al RPMP(12)-a1207 [role of discrete randomness];
    Schuhmacher et al a2004 [quantum simulation];
    > s.a. quantum statistical mechanics [thermalization].
  > Related topics: see dirac equation;
    graph theory and physics; quaternions [quaternion walks].
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