Quantum Entanglement In The System With Atom-field Interaction

Quantum entanglement has been recognized as a useful resource in quantum computer and quantum information processing.Thus the issue of creating, preserving and controlling entanglement has great practical importance in actual quantum information processing.In this dissertation,quantum entanglement in the system with atom-field interaction is investigated.The effects of atomic coherence, Stark shift and detuning on entanglement are investigated,and the optimal system parameters for the genetation of the strong and long-lived entangled state are found.Some significant new results are obtained as follows:In chapter 1,the basic theories of atom-field interaction and quantum entanglement are expatiated.In chapter 2,the sudden death and long-lived entanglement between the two two-level atoms in two-photon and single-photon double JC models are investigated. In a two-photon double JC model,we study the effect of the Stark shift on the entanglement between the two two-level atoms and and that between the two cavity fields,and examine the possibility of controlling the entanglement by the dynamic Stark shift.These results show that the so-called entanglement sudden death can occur if the Stark shift is ignored.However,when the Stark shift is considered,the two atoms are not disentangled at any time,and for large values of the Stark shift parameter,the two atoms can remain in a steady entangled state. In a single-photon double JC model with different coupling constants,we find that the two atoms are in the long-lived entangled states due to difference of the two atom-cavity coupling constants.In chapter 3,the entanglement dynamics in a system of two two-level atoms resonantly interacting with a single-mode thermal field are studied.It is shown that,when the temperature of the cavity is high enough(corresponding to the large value of the mean photon number),the entanglement is greatly enhanced due to the initial atomic coherence,which is helpful for controlling the atomic entanglement by changing the initial parameters of the system,such as the su-perposition coefficients and the relative phases of the initial atomic coherent state and the mean photon number of the cavity field.In chapter 4,quantum entanglement between a binomial field and a cascade three level atom is studied,and the influences of the initial state parameters of the field and the atom on the quantum entanglement are discussed.The results show that quantum entanglement of all states from the coherent state to number state interacting with a cascade three level atom can be displayed by using the binomial field property.Steady field-atom qutrit entanglement state can be prepared via the appropriate selection of system parameters.In chapter 5,the entanglement in a system of a moving∨-type three-level atom interacting with the SU(1,1)-related coherent fields is studied.It is shown that the entanglement depends on the value of field-mode structure parameter p and the difference in photon between the two modes of q,and a maximal atomfield qutrit entanglement state can be prepared via the appropriate selection of system parameters and interaction time.In addition,the entanglement between the moving∨-type three-level atom and the SU(1,1)-related coherent fields and the entanglement between the SU(1,1)-related coherent fields go up and down in a contrary way,and they can impair each other due to the moving three-level atom interacting with the two-mode coherent fields.In chapter 6,the summarization and the prospect are presented.