Interaction Dynamics And Quantum Information Processing For Josephson Junctions And Cavity

In recent years, much attention has been paid to the reseach of superconducting Josephson devices. The ultrasmall josephson junction show obvious quantum character. Such as coulomb blockage of cooper-pair tunnelling,Bloch oscillations, and Zenner tunneling. They can be used to interpret some basic theories of the quantum mechanics.Josephson junction system has the separated energy levels and quantum states as the atom, They behaved the similar properties to atom when derived by the quantized electromagnetic field. Much attention are paid to its applications in technological areas. Quantum computation and information are an active area of mordern physics, people are trying to find physical systems to realize them. Josephson junctions show great superiotity because of its solid character.This paper consists of six chapters. In chapter one, I give a simple overview of the history and realism of research on Josephson junction, and present some basic properties of Josephson junctions. In chapter two, A new scheme to realize quantum logic gates, including CNOT gate and swap gates, and quantum teleportation are described by making use of Josephson junctions. In this scheme, two SQUIDs are controlled by a cavity field and two microwave fileds. In chapter three, entangled properties between SQUID and cavity are investigated in detail. Special attention is paid to thermal entanglement in the system under our consideration. It is shown that the thermal entanglement can be manipulated by varying temperature and an effective controlling parameter B which depends on the external field and characteristic parameters of the system. It is found that there exists a critical value of the controlling parameter Bc. Under a fixed temperature, increasing B can increase entanglement in the regime of B < Bc, while the entanglement decreases with increasing B in the regime of B > Bc. In chapter four, a harmonic oscillator model of a SQUID coupling to quantized cavity field is studied analytically through a unitary transformation approach. An approximate analytic solution is obtained when the SQUID and the quantized cavity field are initially in coherent states. The supercurrent in the SQUID is calculated. It is fond thatthe supercurrent exhists periodical oscilations. In chapter five, preparation of two-particle maximally entangled states is studied by using two inductively coupled SQUIDs. Four two-particle maximally entangled states are obtained explicitly. The last chapter is devoted to conclusion and remarks.