Remote State Preparation In Cavity QED And The Entanglement Of A Two-qubit Heisenberg Spin Model

Quantum information science is the combination of quantum mechanics and information science, which mainly includes quantum computation and quantum communication. Because quantum state is the carrier of information, all the problems related to information should be solved by means of quantum theory. Therefore, quantum information science exhibits a number of advantages in contrast to classical counterpart. To realize quantum information processing scientist need to find a real physical system as the quantum hardware which can realize controllable qubits. Cavity QED system is regarded as one of the most promising systems to realize quantum hardware. The idea of the cavity QED is to trap several atoms in a small high quality cavity. Quantum information can be stored in the internal states of the atoms. The trapped atoms can provide quantum memory and optical cavities can be utilized both to perform quantum gates and to transfer quantum information. Cavity QED system can be used for achieving quantum information processing such as quantum teleportation, the preparation and manipulation of the entangled states, the realization of quantum logic gates, and so on. On the other hand, Heisenberg spin chain as a solid system which realizes qubits has attracted much attention for its scalability and flexibility. It has been widely used to achieve quantum simulation, such as quantum dots, nuclear spins, electric spins, and so on.Based on the technology of cavity QED, we propose two kinds of schemes for remote preparation of a three-atom GHZ class state. Since the cavity used in our schemes is only virtually excited in the interaction process, there is no quantum information transfers between atoms and cavities. So our scheme is immune to both cavity decay and the effect of the thermal field, and the requirement on the quality factor of the cavity is greatly loosened and the efficient decoherence time of the cavity is greatly prolonged. In addition, by choosing appropriate interaction time we need not introduce any additional atoms or cavities which greatly reduce the cost of both quantum and classical resources. In addition, we consider the entanglement of a two-qubit anisotropic Heisenberg XYZ chain in nonuniform magnetic fields with intrinsic decoherence by calculating the concurrence. It is shown that magnetic field has effect on the evolvement of the system for different initial states, the uniform and nonuniform component of the magnetic field play different roles in the evolvement of the system. We also find that the initial state is sensitive to the evolvement of a system, which indicates that the larger concurrence the initial system contains, the higher concurrence the system will retain at last.