Research On Quantum Entanglement And Quantum Discord Dynamics In Bipartite Quantum Systems

Quantum mechanics makes up the deficiencies of classical physics and reveals a number of counter-intuitive effects. In these special physical properties, quantum entanglement is the most inconceivable characteristic of quantum mechanics different from the classical physics. The unique characteristic of quantum entanglement makes the quantum information break through the limit of the classical information, so quantum entanglement has been viewed as the key physical resource of quantum information processing and quantum commutations. Further researches show that quantum entanglement does not account for all the quantum correlations, and the quantum correlations apart from entanglement bring greater advantages for quantum computing and quantum information processing tasks. So quantum discord (QD) as a description of the total information of quantum correlations is introduced.In the quantum information processing tasks, the quantum systems containing the quantum information will unavoidably interact with external environment, leading to decoherence of the system. It is a key obstacle for the fields of quantum information and quantum calculation. However, the researches on the dynamics of quantum systems in various environmental models can help us to acquire the evolutions of quantum system parameters versus the time, which have potential application values in quantum communication and quantum computing.So in this thesis, we focus our research on the quantum entanglement dynamics and the quantum discord dynamics of two-qubit quantum systems, respectively. The two parts are as follows:1. We investigate the dynamical behaviors of two entangled two-level atoms, which interact with a single-mode cavity field and are driven by the classical field. This work mainly study the Tavis-Cummings model in which the dipole-dipole interaction between two atoms and the classical driven strength exist simultaneously. By means of numerical calculations, we detailedly analyze the effect of the classical driven strength, dipole-dipole interaction between two atoms and the detuning between atoms and cavity field on the entanglement dynamical properties of two atoms. Meanwhile, we discuss the optimal region of dipole-dipole interaction between two atoms and the classical driven strength in the case of resonance and off resonance between atoms and cavity field. The result shows that when we choose the appropriate conditions, the phenomenon of entanglement sudden death can be inhibited.2. We investigate the quantum discord dynamics of two atoms resonantly coupled with a dissipative cavity field. The effects of dipole-dipole interaction on the atomic quantum discord has been investigated for a system initial prepared in Bell-like states with the same and different atom-cavity couplings. The result shows that, considering the atomic dipole-dipole interaction, the dipole-dipole interaction can make the atomic quantum discord more robust, and when the strength of dipole-dipole interaction is strong enough, the atomic quantum discord can be improved. In addition, we also analyze the effect of dipole-dipole interaction on dynamical behaviors of the atomic mutual information and classical correlation.