【作者】 胡要花；

【导师】 方卯发；

【作者基本信息】 湖南师范大学 ， 光学， 2009， 博士

【摘要】 量子纠缠已经成为量子计算和量子信息处理过程中的不可或缺的物理资源。量子纠缠态的制备、保持与调控是实现量子计算与量子信息处理的关键问题.本文研究原子与光场相互作用系统中的量子纠缠,考察原子的相干性、双光子过程中的Stark位移、原子跃迁频率之间的失谐量等对原子之间、光场之间、原子与光场之间的量子纠缠的影响,寻找制备高纠缠度、长寿命纠缠态的最佳系统参数条件,得到了一系列有创新意义的结果。第一章阐述原子-光场相互作用的基本理论和量子纠缠的基本理论。第二章研究双光子和单光子双JC模型中的纠缠突然死亡和纠缠持续现象。在双光子双JC模型中,考察Stark位移对原子纠缠和腔场纠缠的影响,研究用Stark位移控制原子纠缠的可能性。结果发现:忽略Stark位移时,原子纠缠出现突然死亡现象;考虑Stark位移时,此系统中的两原子不会出现退纠缠态,特别是当Stark位移参数取值较大时,两原子能保持稳态纠缠。在单光子双JC模型中,两原子与各自相互作用的光场之间经由不同的耦合常数相互作用,结果发现,耦合常数的不同使得两原子出现了长时间的纠缠。第三章研究两个相同二能级原子与单模热光场耦合时两原子间的纠缠动力学,结果表明当腔场温度很高(即模热光场的平均光子数取很大的值)时,原子的初始相干性导致原子纠缠显著增强。通过调节系统的初始参量,例如原子的初始相干程度、相对相位以及单模热光场的平均光子数,可以调控两原子间的纠缠程度。第四章研究二项式光场与级联三能级原子的量子纠缠,讨论了光场与原子的初始参量对其量子纠缠性质的影响。结果表明,利用二项式光场的特性,可以揭示从相干态到数态之间的所有态光场与三能级原子相互作用时的量子纠缠性质。选择适当的系统参数可以制备稳定的光场-原子qutrit纠缠态。第五章讨论一个运动的∨型三能级原子与关联的双模SU(1,1)相干态场相互作用系统中的量子纠缠。结果发现系统中的量子纠缠动力学极大依赖于场模结构参数p和模间光子数之差q。通过选择合适的系统参数和相互作用时间,可以制备原子-光场的qutrit最大纠缠态。此外,原子与双模SU(1,1)相干态场之间纠缠的增强或减弱总是与双模SU(1,1)相干态场的模间纠缠相反,两种纠缠相互制约。第六章对全文进行了总结和展望。更多还原

【Abstract】 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.更多还原