Theoretical Studies On Quantum Correlation And Quantum Features In Open Quantum System

Quantum information theory is a burgeoning interdiscipline between the quantum me-chanics and the information science. It mainly consists of quantum computation, quantum communication and so on. Because the quantum entanglement or quantum correlation is re-quired in most of the quantum information tasks, they are regarded as an important physics resource. So the quantification of such a physics resource becomes an important issue in quantum information theory. In addition, quantum entanglement and quantum correlation are the fundamental physical features by which quantum mechanics is distinguished from the classical mechanics. In practical scenario, due to unavoidable interaction with surround-ings, most of quantum features such as entanglement, quantum correlation, quantum speed limit and quantum Fisher information could be influenced to different extents. Thus it is meaningful both in theory and in practice to study how the surroundings affect quantum en-tanglement, quantum correlation and other quantum features. In this thesis, on the one hand we study quantum entanglement and quantum correlation from the angle of the fundamental principles; On the other hand, based on the concrete systems, we study how the surroundings influence the quantum features such as quantum speed limit and quantum Fisher information and so on.In Chapter 1, we introduce the background of this thesis, and in Chapter 2, we introduce the preliminary concepts and knowledge. The main works are given in Chapters 3 to 7, it can be divided into two parts. The first part consists of Chapters 3,4 and 5, we investigate the measures and application of quantum entanglement and quantum correlation. In Chapter 3, we define a localized quadripartite entanglement according to whether the reduced entangle-ment can be localized, and find that the GHZ state is not only the state that has nonzero localized quadripartite entanglement and the W state is not only the state that has vanishing localized quadripartite entanglement. In Chapter 4, we investigate the quantum correlation in entanglement distillation protocols. In Chapter 5, based on the quantum skew information theory, we firstly define a nonlocality measurement:uncertainty induced nonlocality, which preserves the good computability and satisfies the contractivity; Then, we define a high di-mensional quantum correlation measure by using the joint diagonalization technology. We can obtain analytical expression of quantum correlation for arbitrary m(?)n dimensional sys-tem; In the end, we investigate the quantum consumption in weak measurement processing based on quantum skew information theory.The second part consists of Chapters 6,7. In Chapter 6, we define an initial-state dependence of the quantum speed limit, and find that, apart from that the non-Markovianity and the population of excited state, the initial state of the system is an important factor of the quantum speed limit. In Chapter 7, we investigate the effects of reservoir squeezing on the quantum Fisher information with the interaction (?+b?+?-b??(?)) and ?z(b?+b?(?)) .Compared with the non-squeezed environment, the decay of the quantum Fisher information can be suppressed through adjusting the squeeze parameter r and ?.The summary and prospection are given in Chapter 8.