Generation And Measurement Of Entanglement

The entanglement is an important resource in the fields of quantum computation and quantum information. The thesis discusses the preparation and the measure of some kinds of the quantum entanglement.Firstly, the generation of the entanglement between two two-level atoms interacted with the third atom driven by white noise is investigated when the coupling between atoms is modulated by a pulse function. It is found that the initial triggering time and the width of the pulse can generate a peak in the entanglement. There is an optimal width of the pulse that the entanglement can reach a maximum. The asymmetry of the coupling between atoms can generate different entanglement in the system. The multiple triggers can generate multiple peaks in the entanglement. The separation between two peaks is increased as the width of the pulse is increased.Secondly, the bipartite and tripartite entanglement of a Heisenberg XY model with a nonuniform magnetic field is studied. There are two or four peaks in the concurrence of the bipartite entanglement when the amplitudes of the magnetic fields are differently distributed between the three qubits. It is very interesting to note that there is no tangle of tripartite entanglement between the three qubits when the amplitudes of the magnetic fields are varied. However, the variation of the magnetic field direction can induce the tangle. The tangle is periodic about the angle between the magnetic field and the z axis of the spin.