Theoretical Study Of Quantum Correlations In Cavity QED Systems

Quantum information theory s a rising interdisciplinary field, which is a inevitably result to generalize classical information theory to the quantum world. Starting from the end of the20th century, because of its huge potential applications in military, science and industries, the governments spend a lot of manpower and material resources on this field. Quantum informa-tion theory includes quantum teleportation, quantum computation, quantum superdense coding, quantum remote state preparation, quantum cryptography, and so on. In the quantum information theory, since quantum correlation as a resource plays a very important role in different quantum quantum tasks, it has become a hot topic of theoretical and experimental study in recent years. The study of the preparation, storage, controlling and transmission of quantum correlations, Scientists have mainly focused on some qubit systems with scalability, such as:cavity quantum electrodynamics (QED), quantum dots, spin system, superconducting Josephson junction, and so on. Thereinto, cavity QED is considered as one of the more promising systems to realize quan-tum hardware. The main work of this thesis can be divided into two aspects, in the first aspect, we investigate the quantum correlation dynamics for different dissipative cavity QED systems, and prevent or minimize the influence of environmental noise on target qubits by applying the dynamical decoupling technology.We investigate the quantum discord dynamics for the system consisting of two noninter-acting two-level atoms, each trapped inside a dissipative cavity and find that in some specific initial conditions, the quantum discord between the two atoms can keep constant for a finite time interval which means that the phenomenon of sudden transition between classical and quantum decoherence could arise. It is worth pointing out that the time in which the quantum discord keeps constant is very important for quantum information tasks which base on quantum correlations. Furthermore, it is clearly to see that after the long interaction time, the total correlation, classi-cal correlation and quantum discord of two atoms will tend to a stable value. In particular, the quantum discord of the two atoms is completely unaffected by the dissipation of the cavities if we choose the suitable ratio,which depends on the decay rate of two cavities and the atoms-field coupling constant.We also investigate the dynamics of quantum discord of two atoms which is trapped in a common dissipative cavity and show that for different initial states,the behavior of quantum discord of two atoms is quite different. Then we also discuss that the the quantum discord induced by the dissipation of the cavity and find that the non-zero quantum discord between two atoms can be induced during the time evolution.How to prolong the transition time of quantum discord in quantum information science is very significant because it offers more time for the implementation of quantum information processing. Here, we propose a scheme of prolonging the transition time by means of the dy-namical decoupling pulses. We investigate the quantum discord dynamics between two qubits, each inserted in its own finite-temperature environment with1/f spectral density. It is shown that the phenomenon of sudden transition between classical and quantum decoherence could appear in this system and the transition time depends on the initial-state of two qubits, the qubit-environment coupling constant and the temperature of the environment. In particular, the transi-tion time of quantum discord between two qubits can be prolonged by applying the dynamical decoupling pulses. Moreover, a scheme of entanglement and entangled state transfer between remote cavities via optical fibers has been considered. By comparing the influence of different initial parameters on the transmission scheme, we can find a perfect transfer can be realized if we choose the suitable parameters.On the other aspect, we study that the amount of quantum correlation between two atoms can be controlled and increased by applying the nonlinear Kerr-like medium, and the arbitrary bipartite stationary state quantum correlation of the system could be improved by applying non-linear Kerr-like medium and dipole-dipole interaction in the presence of phase dissipation.We first investigate How to use the nonlinear Kerr-like medium and dipole-dipole interaction to control and increase the quantum entanglement and quantum discord between two atoms, each atom is trapped inside a single-mode optical cavity. It is shown that for some certain initial conditions, entanglement of two atoms disappears suddenly which means that the entanglement of the system keeps zero for a period of time.Because the time in which without entanglement is harmful for entanglement-based quantum information tasks, many efforts have been devoted to eliminating this phenomenon. Here, we find that the duration of entanglement sudden death can be decreased, and the amount of quantum discord and quantum entanglement can be enhanced by adjusting the value of Kerr medium. Particularly, the phenomenon of entanglement sudden death disappears if the value of the Kerr coefficient is large enough.we also discuss that the nonlinear Kerr-like medium and dipole-dipole interaction affect the entanglement sudden death phenomenon and the three-partite entanglement of the system which consists of two two-level atoms are trapped inside a common optical cavity. It is clearly to see that the phenomenon of entanglement sudden death can be weakened by applying the nonlinear Kerr-like medium and dipole-dipole interaction, and the impact of nonlinear kerr-like medium is much stronger than the dipoledipole interaction. Next, we also find that the time in which the three-partite entanglement appears could be tuned by adjusting the values of kerr coefficient and dipoledipole interaction.In addition,we investigate the influence of nonlinear Kerr-like medium and dipole-dipole interaction on the dynamics of quantum discord for different cavity systems with phase dis-sipation. It is shown that the effect of phase dissipation on the system which consists of two noninteracting two-level atoms, each atom is trapped in a optical cavity can be suppressed and the amount of quantum discord can be improved by applying the nonlinear Kerr-like medium. We can also weaken the influence of phase dissipation on the system consisting of two two-level atoms which are trapped in a common optical cavity, and enhance the stationary state quantum discord of the arbitrary bipartite of the system by adjusting the values of Kerr coefficient and dipole-dipole interaction.