الفهرس 
Quantum informationOnly 14 pages are availabe for public view
 |  | from | 158 |  |  |
| | | from | 158 | | |
Abstract
In this thesis, which consists of an introduction in two chapters and another six chapters, we study several effects on quantum information and quantum entanglement through, the interaction between atomic systems described by one or two two-level atoms and quantized radiation field, with one or two modes. In chapter 1, we give an overview of quantum information theory, its importance, history and development in the first section. In the following sections we introduce qubit, density operator, and quantum entanglement, some measures of entanglement for bi-partite system such as von Neumann entropy, negativity and tangle. Furthermore, we define Fisher information: historical importance in statistical and physics, classical and quantum Fisher information. Finally, we end this chapter with a brief qualifier of Fisher information flow. In chapter 2, we discuss briefly about the interaction between atom and radiation field, especially about Jaynes--Cummings model (JC) and its importance in the field of quantum optics. In section 2, we remind ourselves with some states of radiation field to be mentioned in this thesis: Fock state, coherent state, Two mode squeezed state and SU(1,1) coherent state In chapter 3, an analytical description for the dynamics of a two-level atom coupled to field mode in dissipative cavity. The effects of thermal photon on entanglement and information are investigated for atom initially prepared in a coherent superposition of its states and the cavity mode in coherent state. We have used time evolution of atomic quantum Fisher information and von Neumann entropy as indicator and measure of entanglement dynamics respectively through our investigation. In chapter 4, the effect of atomic spontaneous decay is considered for a two-level atom interacting with a single mode of electromagnetic field. The exact solution of the master equation is found by using the dressed state (D-S) representation for atom initially prepared in excited state while the radiation field in a coherent state. We study the effects of atomic decay on information and entanglement through temporal evolution of atomic quantum Fisher information, partial entropy of the atom and negativity for the whole system. In chapter 5, the system of two two-level atoms interacting with a single-mode quantized electromagnetic field in a lossless resonant cavity via a multi photon transition is considered. Two two-level atoms and the field are prepared in the excited atomic state states and coherent state respectively. We investigate the quantum Fisher information, negativity and reduced von Neumann entropy for the two atoms. The classical Fisher Information for the field is examined also. The number of photon transitions plays an important role in the dynamics of different information quantifiers in the cases of two symmetric and two asymmetric atoms. In chapter 6, we investigate the evolution of the quantum Fisher information and its flow based on quantum state estimation in the framework of the interaction between a two-level atom and two-mode squeezed field in a phase damped cavity. The analytical solution for this system when the atom is initially prepared in a superposition state and the field in a two-mode squeezed coherent state is obtained. The entanglement or nonlocal correlations between a mode-mode and two-level atom with two-mode squeezed field is quantified by the field and atomic tangle respectively. The total tangle is used as a quantifier of the entanglement between the system (atom-field) and environment. The effect of the phase damping parameter of the quantum Fisher flow and atom-field entanglement are examined during the time evolution. Finally, we explore the relation between quantum Fisher information its flow and entanglement. In chapter 7, two interacting qubits in different environments varying between dispersive and dephasing environments are considered; the qubits are initially prepared in a mixed state. An analytical solution of the master equation was obtained. The feature of sudden death and rebirth periods of entanglement is discussed under the effect of the different models of environments, we compare between temporal evolution of atomic quantum Fisher information and negativity as a measure of entanglement. In chapter 8, a system described by a nonlinear Janes-Cumming model in the presence of nonlinear quantum dissipation is considered. The field is to be initially in SU (1,1) coherent states and the atom is initially in superposition state. The effect of nonlinear dissipation on information and entanglement of atom-field system is studied by using quantum Fisher information (QFI) and von Neumann entropy. QFI can be used to obtain information from the atom and be used as complementary of entropy and may be considered as an indicator of entanglement. Finally, we conclude our work where we summarize all the results achieved from the previous chapters.