2,508 research outputs found

    Communication Complexity Protocol for Q-trits

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    Consider a function where its entries are distributed among many parties. Suppose each party is allowed to transmit only a limited amount of information to a net. One can use a classical protocol to guess the value of the global function. Is there a quantum protocol improving the results of all classical protocols? Brukner et. al. showed the deep connection between such problems and the theory of Bell's inequalities. Here we generalize the theory to trits. There the best classical protocol fails whereas the quantum protocol yields the correct answer.Comment: 8 page

    Systematic errors due to linear congruential random-number generators with the Swendsen-Wang algorithm: A warning

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    We show that linear congruential pseudo-random-number generators can cause systematic errors in Monte Carlo simulations using the Swendsen-Wang algorithm, if the lattice size is a multiple of a very large power of 2 and one random number is used per bond. These systematic errors arise from correlations within a single bond-update half-sweep. The errors can be eliminated (or at least radically reduced) by updating the bonds in a random order or in an aperiodic manner. It also helps to use a generator of large modulus (e.g. 60 or more bits).Comment: Revtex4, 4 page

    A Spinorial Formulation of the Maximum Clique Problem of a Graph

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    We present a new formulation of the maximum clique problem of a graph in complex space. We start observing that the adjacency matrix A of a graph can always be written in the form A = B B where B is a complex, symmetric matrix formed by vectors of zero length (null vectors) and the maximum clique problem can be transformed in a geometrical problem for these vectors. This problem, in turn, is translated in spinorial language and we show that each graph uniquely identifies a set of pure spinors, that is vectors of the endomorphism space of Clifford algebras, and the maximum clique problem is formalized in this setting so that, this much studied problem, may take advantage from recent progresses of pure spinor geometry

    Anomalous diffusion at percolation threshold in high dimensions on 10^18 sites

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    Using an inverse of the standard linear congruential random number generator, large randomly occupied lattices can be visited by a random walker without having to determine the occupation status of every lattice site in advance. In seven dimensions, at the percolation threshold with L^7 sites and L < 420, we confirm the expected time-dependence of the end-to-end distance (including the corrections to the asymptotic behavior).Comment: 8 pages including figures, presentation improved, for Int.J.Mod.Phys.

    Molecular dynamics simulations of ballistic annihilation

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    Using event-driven molecular dynamics we study one- and two-dimensional ballistic annihilation. We estimate exponents ξ\xi and γ\gamma that describe the long-time decay of the number of particles (n(t)∼t−ξn(t)\sim t^{-\xi}) and of their typical velocity (v(t)∼t−γv(t)\sim t^{-\gamma}). To a good accuracy our results confirm the scaling relation ξ+γ=1\xi + \gamma =1. In the two-dimensional case our results are in a good agreement with those obtained from the Boltzmann kinetic theory.Comment: 4 pages; some changes; Physical Review E (in press

    Complementary algorithms for graphs and percolation

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    A pair of complementary algorithms are presented. One of the pair is a fast method for connecting graphs with an edge. The other is a fast method for removing edges from a graph. Both algorithms employ the same tree based graph representation and so, in concert, can arbitrarily modify any graph. Since the clusters of a percolation model may be described as simple connected graphs, an efficient Monte Carlo scheme can be constructed that uses the algorithms to sweep the occupation probability back and forth between two turning points. This approach concentrates computational sampling time within a region of interest. A high precision value of pc = 0.59274603(9) was thus obtained, by Mersenne twister, for the two dimensional square site percolation threshold.Comment: 5 pages, 3 figures, poster version presented at statphys23 (2007

    Information-Based Physics: An Observer-Centric Foundation

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    It is generally believed that physical laws, reflecting an inherent order in the universe, are ordained by nature. However, in modern physics the observer plays a central role raising questions about how an observer-centric physics can result in laws apparently worthy of a universal nature-centric physics. Over the last decade, we have found that the consistent apt quantification of algebraic and order-theoretic structures results in calculi that possess constraint equations taking the form of what are often considered to be physical laws. I review recent derivations of the formal relations among relevant variables central to special relativity, probability theory and quantum mechanics in this context by considering a problem where two observers form consistent descriptions of and make optimal inferences about a free particle that simply influences them. I show that this approach to describing such a particle based only on available information leads to the mathematics of relativistic quantum mechanics as well as a description of a free particle that reproduces many of the basic properties of a fermion. The result is an approach to foundational physics where laws derive from both consistent descriptions and optimal information-based inferences made by embedded observers.Comment: To be published in Contemporary Physics. The manuscript consists of 43 pages and 9 Figure

    A Formal Definition of SOL

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    This paper gives a formal definition of SOL, a general-purpose algorithmic language useful for describing and simulating complex systems. SOL is described using meta-linguistic formulas as used in the definition of ALGOL 60. The principal differences between SOL and problem-oriented languages such as ALGOL or FORTRAN is that SOL includes capabilities for expressing parallel computation, convenient notations for embedding random quantities within arithmetic expressions and automatic means for gathering statistics about the elements involved. SOL differs from other simulation languages such as SIMSCRIPT primarily in simplicity of use and in readability since it is capable of describing models without including computer-oriented characteristics

    The Mott insulator phase of the one dimensional Bose-Hubbard model: a high order perturbative study

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    The one dimensional Bose-Hubbard model at a unit filling factor is studied by means of a very high order symbolic perturbative expansion. Analytical expressions are derived for the ground state quantities such as energy per site, variance of on-site occupation, and different correlation functions. These findings are compared to numerics and good agreement is found in the Mott insulator phase. Our results provide analytical approximations to important observables in the Mott phase, and are also of direct relevance to future experiments with ultra cold atomic gases placed in optical lattices. We also discuss the symmetry of the Bose-Hubbard model associated with the sign change of the tunneling coupling.Comment: 7 pages, 4 figures, 1 table. Significantly expanded version with respect to former submission (to appear in Phys. Rev. A

    SOL - A Symbolic Language for General-Purpose Systems Simulation

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    This paper illustrates the use of SOL, a general-purpose algorithmic language useful for describing and simulating complex systems. Such a system is described as a number of individual processes which simultaneously enact a program very much like a computer program. (Some features of the SOL language are directly applicable to programming languages for parallel computers, as well as for simulation.) Once a system has been described in the language, the program can be translated by the SOL compiler into an interpretive code, and the execution of this code produces statistical information about the model. A detailed example of a SOL model for a multiple on-line console system is exhibited, indicating the notational simplicity and intuitive nature of the language
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