Quantum Entanglement and Quantum Discord in a Spin Ladder
|Keywords||spin ladder quantum entanglement quantum discord|
Since the quantum entanglement is one of the important resources in quantum information and quantum computation, it has been attracted much attention. In this thesis, the generation and storage of quantum entanglement, the dynamics of quantum discord in a system of two qubits coupled to a spin ladder are discussed.Firstly, the total Hamiltonian of two qubits coupled to a spin ladder is reduced to an effective Hamiltonian of the two qubits. By calculating the entanglement of the two qubits, it is found that the entanglement is a periodic function of time and oscillates between 0 and 1. It is interesting that the maximum entanglement can exist for quite long time when the number of spins in the ladder is increased and there is an external magnetic field. By adjusting some parameters of the system, the plateau in the entanglement can appear. During this period, high entanglement in the system can be kept. The entangled states can be stored. It is quite suitable for quantum computation and quantum communication.Secondly, the quantum discord of two qubits coupled to a spin ladder is studied. For two-side coupling, the quantum discord shows funnel shapes as a periodic function of the initial state and the time. At any initial state, the quantum correlation can reach and be close to the maximum. It is quite suitable for quantum information processing. For one- side coupling, the quantum discord can be simply described by measurement induced disturbance (MID). The MID oscillates and decays with time. The first peak in MID does not last very long. It seems that it is not suitable for quantum information processing.