| Quantum information science resources from the combination of principles of quantum mechanics with information theory and computation science. All procedures of information transformation and computation must be carried out with objects obey-ing laws of physics, and the most important element of quantum information is qubit. Parallel with it classical counterpart, one of the ultimate targets of quantum information is quantum computer. Lessons in quantum information have deepen our understanding of quantum mechanics, One example in point is quantum entanglement. In fact, it is the result of supposition of quantum states. Entanglement is the building block of quan-tum information and computation. Decoherence, which is a fundamental problem in quantum mechanics, is a devastated blow over quantum information processing. It is induced by the avoidable coupling between the system and environment, and methods developed to fight against decoherence is compulsory for quantum information tasks. So researches in quantum information science has shaped our knowledge of decoher-ence. Besides, researches in quantum information science is useful when it comes to quantum many-body problem, as we have learned that the difficulty in many-body sys-tem lies in the ample entanglement among them.Ratchet effect is the phenomenon of creating out directed current from a periodic system without macroscopic bias, and it was the result of symmetry breaking. At a first sight, it is conflicting with the second law of thermodynamics. In fact there is a closed relationship between them, and researches in ratchet effect has helped to deepen our outstanding of the second law of thermodynamics from. With the development of manufactural, exquisite structures with microscopic asymmetry could be set up induced directed transport at different system. So researched conducted on ratchet effect is valuable for both fundamental research and our daily life. With the adventure of optical lattice, coherence quantum ratchet is possible. The main structure and results of our dissertation are as follows:1, Partial-measurement induced entanglement dynamics in Superconducting qubits.Superconducting qubit is a promising candidate for both considerate quantum computation and quantum computer. We find continuouly partial mesurement can in-duced entanglement sudden birth for the phase qubits system, through our theoretical research on periodical measurement on one side of the superconducting circuit. Mea-surement should not always make entamglement weaker. We find that for a family of mixed state, a pure state can be take out with the help of the continuously partial measurement.2, Correlation dynamics of the spin-boson model.Decohence is due to the coupling of system and environment. In order to fight against deocherence, we need to learn them first. For the system composed of two spins suffers from reservoir composed of bosons. With the help of collective states, with get the analytic solution of the whole system. We look into the transition of the correlations for the spin system and the reservoirs, and find at the end of revolution all correlation in the spin system transfer into the reservoirs.3, Spin dynamics of the one dimensional XY model.Through the dynamics of correlations between different site, after the whole sys-tem suffered from quenching. we find that the dynamics of correlation can be used to indicating the quantum phase transition. What is more, w find that it is the dynamics of classical correlation which can be used to indicating the quantum phase transition.4, A new scheme for quantum flashing ratchet.We improve the quantum flashing ratchet by inducing time asymmetry, at the same time keep the period of the ratchet unchanged. This model can help us to induced directed current that the original would not. For our improved scheme, high order quantum resonance can be stimulated to display directed current more efficiently. |
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