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The Quantum Entanglement Properties in a System Interacting Two Entangled Atoms with Several Typical Light Field

Author: ZhangCaiHua
Tutor: SaChuErFu
School: Inner Mongolia Normal
Course: Optics
Keywords: quantum optics quantum entanglement moving atoms atoms in bell state squeezed coherent state Schr?dinger cat state coherent state
CLC: O431.2
Type: Master's thesis
Year: 2009
Downloads: 87
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Abstract


Quantum entanglement not only has important significance in knowing the basic concept of quantum mechanics, but also is one of useful information resources in quantum information science. So, the study of the quantum entanglement properties in the system of the atom interacting with the light field has been devoted to considerable attention. In this paper, the quantum entanglements in a system of two entangled atoms interacting with the different light field are studied by means of the full quantum theory. The major content of this thesis is displayed as follows:In chapter one,the theories on quantum entanglement and the method in quantum entanglement measurement are briefly introduced.In chapter two, the quantum entanglement in a system of two entangled atoms interacting with the squeezed coherent state is studied. The influences of the coherent amplitude factor, the squeezing factor, the ratio of two coupling coefficients on the entanglement property are discussed. The results show that two atoms entanglement evolution property is opposed to atom-field entanglement evolution property. The increase of the coherent amplitude factor or the decrease of squeezing factor of light lead to the increase of atom-atom entanglement degree while the decrease of atoms-field entanglement degree and two atoms stay in the steady entangled state. Moreover, the two-atom quantum state will stay in the maximum entangled state when the atomic dipole-dipole coupling coefficient is large enough.In chapter three, the field entropy evolution in a system of two moving entangled atoms interacting with the squeezed coherent state is studied. The influences of the coherent amplitude factor, the squeezing factor, the atomic motion and the field-model structure parameter on the field entropy are discussed. The results show that an increase of coherent amplitude factor weakens the degree of entanglement between the atoms and the light field. However, an increase of squeezing factor of light strengthens the degree of entanglement between the atoms and the light field.In chapter four, the field entropy evolution of a system interacting two moving entangled atoms with the Schr?dinger cat state is studied .The influences of the strength of light field, the phase angle between the two coherent states, the atomic motion and the field-model structure parameter on the field entropy are discussed. The result shows that when the strength of light field is small, the degree of entanglement is maximum in a system of the moving atoms interacting with an odd coherent state; it is intermediate for a system of the moving atoms interacting with Yurke-Stoler coherent state, and it is minimum in a system of the moving atoms interacting with an even coherent state. When the strength of light field is large enough,the degrees of entanglement between the moving atoms and the three different states of the light field become equal, and the properties of field entropy evolvement are also same.In chapter five, the field entropy evolution in a system which is composed of two moving atoms in bell state interacting with the coherent state is studied. The influences of the different initial states of two atoms, the strength of light field, the atomic motion and the field-model structure parameter on the field entropy are discussed. The result shows that the quantum field entropy does not change with the time and always remains at zero when the two atoms are initially in the bell state |β11〉, the field is completely disentangled from the atoms. The quantum field entropy evolves periodically with the time, when the two atoms are initially in the bell state |β00〉, |β10〉or |β01〉, the field periodically entangled with the atoms. In the latter case, with the increasing of the strength of light, the field entropy is increased for the bell state |β01〉, while the field entropy is decreased for the bell state |β00〉or |β10〉. In the case, the atoms-field entanglement degree sensitively depends on the strength of light for the bell state |β10〉.The atomic motion leads to the periodic evolution of the field entropy. With increasing atomic speed or field-model structure parameter, the evolution period of the field entropy is shorter, and the degree of entanglement between field and moving atoms becomes small.

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CLC: > Mathematical sciences and chemical > Physics > Optics > The light nature of the theory > Quantum optics
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