Quantum Discord For Two-body Systems And Persistence Under Dissipative Processes

With the rapid development of quantum mechanics, mathematics and information science, the cross-disciplinary subject of quantum information has been established. During the development, quantum entanglement which is the quantum property of quantum mechanics has played a very important role. Therefore, it is very important to have a better understanding about quantum entanglement in the development of quantum information science. The attentions of study now have been focused on quantum entanglement as well as quantum correlation in the interacting quantum systems. In this paper, we will discuss the measurement about quantum entanglement and quantum correlation.In the measurements of quantum entanglement, only two-body entanglement measure had been developed relatively clear. That is Concurrence, defined by Wootters, which can be used to measure two-body systems in either mixed states or pure states. In the first chapter of the paper, quantum entanglement and its measurement - Concurrence will be introduced.With the in-depth understanding of the quantum correlation, it was suggested that quantum entanglement does not include the full information of quantum correlation. Another measurement, called Quantum Discord, which was obtained by measuring may contain complete quantum information of the interacting quantum systems. In the second chapter, Quantum Discord is introduced.So far, Quantum Discord was only discussed in two-body systems. But it has been used in many studys. Such as, Grover search, quantum phase transition and a deterministic quantum computation with one pure qubit.The property of this measurement will be discussed in this paper. In the third chapter, we will study the Quantum Discord of two-body state which has been selected. In the pure states we selected, Quantum Discord is equal to the entanglement of formation. The channels under Markovian environment will be involved in the fourth chapter, which transform the pure states into mixed states. And the variation of Quantum Discord under the channels will also be discussed. In the fifth chapter, the Concurrence of the states introduced in the chapter three and four will be computed, and by comparing Quantum Discord with Concurrence we will obtain that Quantum Discord sudden death can't be found in these mixed states.