Study On Different Quantum Properties In A System Of Two Coupled Two-level Atoms Interacting With A Single Mode Thermal Field

The dissertation focuses on the quantum properties in a system of two two-level atoms interacting with a single-mode thermal field,and discusses the time evolution of quantum entanglement,quantum coherence,linear entropy,quantum correlation and classical correlation under different initial conditions.The specific contents are as follows:1.The concepts of quantum entanglement,quantum coherence(C_l1),linear entropy(S),quantum discord(QD),geometrical quantum discord(GQD)and classical correlation(CC)are briefly described.2.Using fully quantum theory,the quantum properties in a system of two two-level interacting atoms with a single mode thermal field are investigated.The first atom is isolated and the other is coupled to a single mode thermal field playing the role of a small external environment in this simple model.By accurately solving the model,the influence of the small external environment on the quantum characteristics in a system of two interacting two-level atomic systems is analyzed.The time evolution of quantum entanglement and coherence in the considered system is presented.The effects of the correlation coupling constant and the ambient effective temperature on the time evolution of the relevant physical quantities are discussed.The results show that the sudden death and birth of quantum entanglement between two atoms in the system can be observed.As the mean photon number is at the different values,the coherence and atomic linear entropy also show different evolution behavior with time going on in both the weaker and the stronger coupling conditions.3.Using the concepts of quantum entanglement,quantum correlations and classical correlation and the method of full quantum theory,the evolution properties of quantum entanglement,quantum discord,geometrical quantum discord and classical correlation in a system of two coupled two-level atoms interacting with a single mode electromagnetic field in a thermal state are studied under the certain conditions.When the two atoms are in the separated state at the initial time,we analyze the effects of the coupling strength between the two coupled two-level atoms and a single mode radiation field in a thermal state.At the same time,we also discuss the mean photon number on the evolution properties of quantum entanglement,quantum correlations and classical correlation between the two atoms in the system.The results show that when atom weakly coupled to thermal field,the evolution of quantum entanglement,quantum discord and geometrical quantum discord between two coupled two-level atoms presents the phenomenon of sudden death and sudden birth with the increase of the mean photon number of a single mode radiation field in a thermal state,which exhibit a collapse-revival process with gradually decreasing amplitude in the long time scale,and the evolution of classical correlation shows a stable oscillation form.When the effective coupling constant between the atom and a single mode electromagnetic field in a thermal state is stronger,the changes of quantum entanglement and quantum correlations will still show the phenomenon of sudden death and sudden birth with increase of the mean photon number of a single mode radiation field in a thermal state.The four quantities are all in the form of irregular oscillation and the values of them are significantly reduced in the long time scale.It is found that the other quantum corrections remain in the absence of quantum entanglement in the observed period of time.4.We study the time evolution behavior of entanglement,the quantum and classical correlations in a system of two coupled two-level atoms interacting with a single mode thermal field.In the model,one atom is in an isolated state and the other is coupled with a small external environment(a single mode thermal field).The effects of mean photon number of thermal field,atom-field coupling strength and intensity-dependent coupling on the evolution processes of the four quantities are analyzed and discussed thoroughly.The results show the sudden deaths and sudden births of various correlations occur and quantum correlation beyond entanglement may be observed in the certain time intervals.It has been seen clearly that the maximal values of various correlations degrade with the increase of mean photon number,atom-field coupling strength and intensity-dependent coupling.The evolution patterns of various correlations are strongly dependent on the about three parameters.Particularly,the time evolution of classical correlation is not consistent with that of quantum correlations during the observed period of time.