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Study on Quantum Entanglement of Atomsystems under Different Conditions
Author: ChenZuo
Tutor: SongHeShan
School: Dalian University of Technology
Course: Theoretical Physics
Keywords: Quantum Entangled States Master Equation Quantum Noise A Spin1/2 Approximation Method Quantum Gate
CLC: O413
Type: PhD thesis
Year: 2007
Downloads: 242
Quote: 1
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Abstract
The preparation of quantum entangled states and quantum decoherence are two important subjects in quantum information and are fundamental to quantum communicationand quantum computers. The development of quantum information both in theory and inexperiment indicates that quantum entangled states are indispensable resources in quantum information processes such as quantum teleportation, quantum information storage, etc.Therefore, quantum information demonstrates its significance only when entangled qubits,convenient for integration, storage and manipulation, are realized in experimentallyaccessiblephysical systems. On the other hand, if the effects of the environment are taken into account,the interaction of the system in question and the environment will inevitably cause decoherence. Thus, the study of the process of the decoherence is very important for the theory andpractice of quantum information. Environment is often treated as noise in quantum information. Accordingly, study on the issue of the decoherence and quantum noise is fundamentalto applications of the quantum information theory.The motivation of this dissertation arose from the abovestated important role of quantum entanglement in quantum information. In this dissertation, the question on quantumentanglement of atomsystem under several different conditions is discussed. In the first threechapters, quantum information is briefly reviewed. Some basic quantum theories on quantumentanglement and master equation are discussed, including the definition, measurement andrealization of quantum entangled states and the derivation and solution of the master equations. The above discussions consist of the background for this dissertation. From Chapter4 to Chapter 6, several possible schemes on the generation and application of atomsystementangled states are put forward and discussed under several different conditions. In detail,the influence of quantum noise on quantum entangled states is studied in Chapter 4. Generally speaking, noise is negative for quantum information processes. However, noiseassistedentanglement preparation is investigated and it is found that noise may play a positive rolein entanglement generation. The dependence of the entanglement on the noise intensity aswell as on other parameters in the model is studied both analytically and numerically: theamount of entanglement behaves as monotonic function of the atom decay rate, and reachesits maximum value for an intermediate noise intensity. The results show that the interaction of system with noise is the important factor for entanglement generation. In Chapter 5, aspin1/2 approximation method to study the quantum entanglement of twocomponent BoseEinstein condensates trapped in double wells is proposed. The contours of entanglement withrespect to tunneling rate and time are found to be hyperboliclike and nonmonotonic. Inthis chapter, a new method to deal with multiplebody problem and to transform an exact manybody problem to a bipartite twostate problem under the spin1/2 approximationis proposed. The new method greatly reduces the difficulty of the problem. In addition, thecomparison of classical and quantum physics is also discussed. As an application in quantumcommunication of quantum entangled states, a new fundamental quantum gate based on auniversal intrinsic interaction Hamiltonian is constructed in Chapter 6. New operators, thegeneralized pseudospin operators, are introduced and a universal intrinsic Hamiltonian witha twoqubit interaction is studied in terms of these operators. A fundamental quantum gateis constructed based on the universal Hamiltonian and it is shown that the role of the newquantum gate is functionally equivalent to the joint operation of Hadamard and CNot gates.In summary, the quantum entanglement, the core of the quantum information theory,is a potential mechanism for the quantum measurement and decoherence, and is criticallyimportant to the understanding of the boundary between quantum physics and classicalphysics. Therefore, the study of both quantum entanglement and its applications in quantuminformation are significant and necessary not only to the further understanding of the specialproperties of the quantum mechanics but also to the providing of practical physical resourcesfor information transmission and information processing. Some theoretical investigations onquantum entanglement are pursued in this dissertation. Quantum information theory is arapidlydeveloping research field. Further investigations of quantum entanglement will beundertaken in future.

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CLC: > Mathematical sciences and chemical > Physics > Theoretical Physics > Quantum theory
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