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Search Results: 1 - 10 of 44051 matches for " Jinshan Wu "
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Non-equilibrium BBGKY Hierarchy from the Redfield Equation
Jinshan Wu
Physics , 2010, DOI: 10.1088/1367-2630/12/8/083042
Abstract: A BBGKY-like hierarchy is derived from the non-equilibrium Redfield equation. Two further approximations are introduced and each can be used to truncate and solve the hierarchy. In the first approximation such a truncation is performed by replacing two-particle Green's functions (GFs) in the hierarchy by their values at equilibrium. The second method is developed based on the cluster expansion, which constructs two-particle GFs from one-particle GFs and neglects the correlation part. A non-equilibrium Wick's Theorem is proved to provide a basis for this non-equilibrium cluster expansion. Using those two approximations, our method of solving the Redfield equation, for instance, of an N-site chain of interacting spinless fermions, involves an eigenvalue problem with dimension $2^{N}$ and a linear system with dimension $N^2$ in the first case, and a nonlinear equation with dimension $N^2$ in the second case, which can be solved iteratively via a sequence of $N^2$ linear systems. Other currently available direct methods correspond to a linear system or an eigenvalue system with dimension $4^N$ plus an eigenvalue system with dimension $2^N$. As a test of the methods, for small systems with size N=4, results are found to be consistent with results made available by other direct methods. Although not discussed here, extending both methods to their next levels is straightforward. This indicates a promising potential for this BBGKY-like approach of non-equilibrium kinetic equations.
An artificial game with equilibrium state of entangled strategy
Jinshan Wu
Physics , 2004,
Abstract: Using the representation introduced in \cite{frame}, an artificial game in quantum strategy space is proposed and studied. Although it has well-known classical correspondence, which has classical mixture strategy Nash Equilibrium states, the equilibrium state of this quantum game is an entangled strategy (operator) state of the two players. By discovering such behavior, it partially shows the independent meaning of the new representation. The idea of entanglement of strategies, instead of quantum states, is proposed, and in some sense, such entangled strategy state can be regarded as a cooperative behavior between game players.
A new mathematical representation of Game Theory II
Jinshan Wu
Physics , 2004,
Abstract: In another paper with the same name\cite{frame}, we proposed a new representation of Game Theory, but most results are given by specific examples and argument. In this paper, we try to prove the conclusions as far as we can, including a proof of equivalence between the new representation and the traditional Game Theory, and a proof of Classical Nash Theorem in the new representation. And it also gives manipulation definition of quantum game and a proof of the equivalence between this definition and the general abstract representation. A Quantum Nash Proposition is proposed but without a general proof. Then, some comparison between Nash Equilibrium (NE) and the pseudo-dynamical equilibrium (PDE) is discussed. At last, we investigate the possibility that whether such representation leads to truly Quantum Game, and whether such a new representation is helpful to Classical Game, as an answer to the questions in \cite{enk}. Some discussion on continuous-strategy games are also included.
Quantum Prisoner's Dilemma in the new representation
Jinshan Wu
Physics , 2004,
Abstract: Using the representation introduced in our another paper\cite{frame}, the well-known Quantum Prisoner's Dilemma proposed in \cite{jens}, is reexpressed and calculated. By this example and the works in \cite{frame} on classical games and Quantum Penny Flip game, which first proposed in \cite{meyer}, we show that our new representation can be a general framework for games originally in different forms.
A new mathematical representation of Game Theory, I
Jinshan Wu
Physics , 2004,
Abstract: In this paper, we introduce a framework of new mathematical representation of Game Theory, including static classical game and static quantum game. The idea is to find a set of base vectors in every single-player strategy space and to define their inner product so as to form them as a Hilbert space, and then form a Hilbert space of system state. Basic ideas, concepts and formulas in Game Theory have been reexpressed in such a space of system state. This space provides more possible strategies than traditional classical game and traditional quantum game. So besides those two games, more games have been defined in different strategy spaces. All the games have been unified in the new representation and their relation has been discussed. General Nash Equilibrium for all the games has been proposed but without a general proof of the existence. Besides the theoretical description, ideas and technics from Statistical Physics, such as Kinetics Equation and Thermal Equilibrium can be easily incorporated into Game Theory through such a representation. This incorporation gives an endogenous method for refinement of Equilibrium State and some hits to simplify the calculation of Equilibrium State. The more privileges of this new representation depends on further application on more theoretical and real games. Here, almost all ideas and conclusions are shown by examples and argument, while, we wish, lately, we can give mathematical proof for most results.
Hamiltotian Formalism of Game Theory
Jinshan Wu
Physics , 2005,
Abstract: A new representation of Game Theory is developed in this paper. State of players is represented by a density matrix, and payoff function is a set of hermitian operators, which when applied onto the density matrix give the payoff of players. By this formulism, a new way to find the equilibria of games is given by generalizing the thermodynamical evolutionary process leading to equilibrium in Statistical Mechanics. And in this formulism, when quantum objects instead of classical objects are used as the objects in the game, it's naturally leads to the so-called Quantum Game Theory, but with a slight difference in the definition of strategy state of players: the probability distribution is replaced with a density matrix. Further more, both games of correlated and independent players can be reached in this single framework, while traditionally, they are treated separately by Non-cooperative Game Theory and Coalitional Game Theory. Because of the density matrix is used as state of players, besides classical correlated strategy, quantum entangled states can also be used as strategies, which is an entanglement of strategies between players, and it is different with the entanglement of objects' states as in the so-called Quantum Game Theory. At last, in the form of density matrix, a class of quantum games, where the payoff matrixes are commutative, can be reduced into classical games. In this sense, it will put the classical game as a special case of our quantum game.
Theory of Games on Quantum Objects
Jinshan Wu
Physics , 2005,
Abstract: Effect of replacing the classical game object with a quantum object is analyzed. We find this replacement requires a throughout reformation of the framework of Game Theory. If we use density matrix to represent strategy state of players, they are full-structured density matrices with off-diagonal elements for the new games, while reduced diagonal density matrix will be enough for the traditional games on classical objects. In such formalism, the payoff function of every player becomes Hermitian Operator acting on the density matrix. Therefore, the new game looks really like Quantum Mechanics while the traditional game becomes Classical Mechanics.
Heat transport in quantum spin chains: the relevance of integrability
Jinshan Wu,Mona Berciu
Physics , 2010, DOI: 10.1103/PhysRevB.83.214416
Abstract: We investigate heat transport in various quantum spin chains, using the projector operator technique. We find that anomalous heat transport is linked not to the integrability of the Hamiltonian, but to whether it can be mapped to a model of non-interacting fermions. Our results also suggest how seemingly anomalous transport may occur at low temperatures in a much wider class of models.
Kubo formula for finite size systems
Jinshan Wu,Mona Berciu
Physics , 2010, DOI: 10.1209/0295-5075/92/30003
Abstract: We demonstrate that the proper calculation of the linear response for finite-size systems can only be performed if the coupling to the leads/baths is explicitly taken into consideration. We exemplify this by obtaining a Kubo-type formula for heat transport in a finite-size system coupled to two thermal baths, kept at different temperatures. We show that the proper calculation results in a well-behaved response, without the singular contributions from degenerate states encountered when Kubo formulae for infinite-size systems are inappropriately used for finite-size systems.
Could a Classical Probability Theory Describe Quantum Systems?
Jinshan Wu,Shouyong Pei
Physics , 2005,
Abstract: Quantum Mechanics (QM) is a quantum probability theory based on the density matrix. The possibility of applying classical probability theory, which is based on the probability distribution function(PDF), to describe quantum systems is investigated in this work. In a sense this is also the question about the possibility of a Hidden Variable Theory (HVT) of Quantum Mechanics. Unlike Bell's inequality, which need to be checked experimentally, here HVT is ruled out by theoretical consideration. The approach taken here is to construct explicitly the most general HVT, which agrees with all results from experiments on quantum systems (QS), and to check its validity and acceptability. Our list of experimental facts of quantum objects, which all quantum theories are required to respect, includes facts on repeat quantum measurement. We show that it plays an essential role at showing that it is very unlikely that a classical theory can successfully reproduce all QS facts, even for a single spin-1/2 object. We also examine and rule out Bell's HVT and Bohm's HVT based on the same consideration.
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