The Generation, Control And Nonlocality Of Entangled States In The Dissipative Systems

The generation, control and nonlocality of entangled states in thedissipative systemsQuantum entanglement plays an important role in quantum computer and quantum in-formation. It has been recognized as a useful resource in various quantum informationprocesses. While the generation of entanglement can be destroyed by the interactionbetween the system of interest and its surrounding environment in most situations. Inresent years, The generation, control and nonlocality of entangled state in the dissi-pative system have become a hot topic. In this dissertation, the generation, controland nonlocality of atomic entangled state in the dissipative system are investigatedby using the master equation approach. Some significant new results are obtained asfollows.From chapter 1 to 2, the basic theories of master equation approach , quantumentanglement, quantum control and quantum nonlocality are elaborated in the dissi-pative system. Firstly, the basic theories of master equation in the dissipative system,such as the derivation and the solution of master equation, and the master equationof a collective atomic system, are given. Secondly, the methods of classify, measure-ment of quantum entanglement, and the physical implementation of manipulation ofquantum entanglement are presented. Thirdly, the contents of research, the choiceof strategies and algorithms in quantum control are expounded. Finally, the meaning,criterion, and measurement of quantum nonlocality are presented.In chapter 3, quantum entanglement between two spatially separated two-levelatoms driven by an external coherent laser field in the dissipative process of spontaneousemission are studied. It is shown that the entanglement exhibits long-time oscillatorybehaviour with remarkable entanglement in the peaks and the peak and period arerelated to the Rabi frequencies of the external coherent laser field. In chapter 4, the three-body entanglement induced by spontaneous emission inthree two-level atoms system by using the entanglement tensor approach is studied.It is shown that the change of entanglement measures is dependent on the systeminitial state and the classification of atom. The three-body entanglement is the resultof the coherent superposition of the two-body entanglements. The larger the two-bodyentanglements is, the stronger the three-body entanglement is. If the difference of anytwo two-body entanglement is very small, the three-body entanglement is very strong.It is found that the maximum of the two-body entanglement obtained with nonidenticalatoms is greater than that obtained with identical., atoms via adjusting the differenceof atomic frequency.In chapter 5, stationary entanglement between two spatially separated two-levelatoms driven by a coherent laser field in the dissipative process of spontaneous emissionis investigated. It is shown that the entanglement strongly depends on the detuning ofthe laser frequency from atomic transition frequency, the interatomic separation andthe Rabi frequency of the coherent laser field. A considerable amount of stationaryentanglement can be obtained nearΔ=-α(i.e., the dipole-dipole interaction and thedetuning cancel out mutually) for small atomic separation and large Rabi frequency ofthe coherent laser field.In chapter 6, quantum entanglement between two spatially separated atomscoupled to the thermal reservoir is examined. The results show that the maximumof the entanglement obtained with nonidentical atoms is greater than that obtainedwith identical atoms. The degree of entanglement is progressively decreased with theincrease of the thermal noise. Interestingly, the two atoms can be easily entangled eveneach of the two atoms is initially prepared in the most mixed states.In chapter 7, the entanglement and the nonlocality of two qubits collectivelyinteracting with a common thermal reservoir are investigated. It is found that the timebehaviour of these quantities exhibits a strong dependence on the initial state of twoqubits. The collective decay of two qubits can induce stationary entanglement when two qubits are initially in incoherent states. The common thermal resevoir can alsoenhance the entanglement of two qubits when two qubits are initially in coherent states.It is very valuable that it provides us a feasible way to manipulate and control theentanglement and the nonlocality by changing the relative phases and the amplitudesof the polarized qubits in various physical system such as the trapped ions, quantumdots or Josephson Junctions.In chapter 8, the summarization and the hope are presented.