Studies On Quantum Computation And Quantum Correlation In The Josephson Junction Systems

Studies on the implementation of quantum computation and the properties of quan-tum correlation in Josephson junction systems are discussed in this dissertation. It mainly focuses on the following parts.First, we give a brief introduction on quantum computation. Quantum computation is a wide field and develops rapidly. Take the advantage of principles of quantum mechanics, the computational power of quantum computers exceed classical computers largely. Based on quantum computation, lots of hard work in classical computation such as large num-ber factoring can be solved efficiently. Subsequently, we present the status of Josephson junction system and its applications in quantum computation, including two basic imple-mentations of quantum bit based on Josephson junction systems.We describe a topological protected Josephson junction array system. And propose a complete quantum computation scheme on it. The logic qubit for quantum computation is encoded in a punctured array. The number of qubits depends on the number of holes in this system. The topological degeneracy is lightly shifted by tuning the flux along specific paths. As a complete quantum computation scheme, we show how to perform both single-qubit and basic quantum-gate operations in this system, especially the controlled-NOT (CNOT) gate.We study the properties of quantum discord (QD) which is a kind of measurement of quantum correlation in a two-qubit Heisenberg XXZ system with DM interaction. We compare the thermal QD with thermal entanglement in this system and find that QD decrease asymptotically to zero with temperature while entanglement decreases to zero at the point of critical temperature. This phenomenon shows the robust of QD and that QD can be used as a resource. We find behaviors of QD vary opposite to entanglement with some DM parameters and this possibly offers a potential solution to enhance entanglement of certain systems. We also show that tunable parameter Dx is more efficient than parameter Dz in most regions for controlling the QD.Finally, we investigate QD with exotic features discussed above in a two-qubit real Josephson-junction system. We find that QD of such a system in lab correlates closely with temperature and Josephson coupling energy EJ. QD can be enhanced while lowering Ej or temperature. The behavior trends of identical qubits system and distinct qubits system maintain the same. We can get a higher QD when making EJ and temperature smaller. Also we can take a good chance to use such quantum resource when two qubits are identical since in this case we can get more quantum discords.