Realization Of GHZ And W Entangled States With Multiple Superconducting Quantum-Interference Device Qubits In Cavity QED

Quantum Information Science (QIS) is an emerging field with the potential to cause revolutionary advances in fields of science and engineering involving computation, communication, precision measurement, and fundamental quantum science. The roots of this field go back about twenty years, when pioneers such as Charles Bennett, Paul Benioff, Richard Feynman, and others began thinking about the implications of combining quantum mechanics with the classical Turing computing machine.Quantum entanglement is one of the most striking features of quantum physics. Quantum entanglement is also a potential resource for quantum information processing, and can be used to test basic problems in quantum mechanics. Entanglement plays an important role in quantum computation and quantum secret communications, such as quantum cryptography, quantum teleportation, error correction protocols and quantum dense coding. Over the last decade, many schemes for generating various entangled states have been proposed and experimental realizations of entangled states have also been reported. Proposals have been presented for the generation of entangled states using atom beams, ions and photons. In microwave cavity, entanglement with two atoms, three photons and four ions have also been experimentally realized. In recent years, much attention has been attracted to the generation of the entangled states with a large number of qubits, especially to the realizations of the Greenberg-Horne-Zeilinger (GHZ) and W type of entangled states. Several schemes have been proposed to generate the GHZ and W type of entangled states in some physical systems and models, such as atom-cavity quantum electrodynamics (CQED), ion well, nuclear magnetic resonance (NMR), linearity optics device, semiconductor quantum dot, Heisenberg XY model and four-wave-mixing (FWM). In contrast to these physical systems, RF superconducting quantum-interference device (SQUID), as a solid state qubits, are of particular interest because of their potential suitability for integrated devices. Comparing with other systems it can be scaled up and demonstrated to have long decoherence time.The primary work is described as following:In the first part, we introduce quantum entanglement and the coupling model of cavity and SQUID.In the second part, we present two schemes of generating GHZ and W entangled states.In the first scheme, we placed large amount of three-levelΛ-type SQUID qubits into cavity QED. First let us consider a system composed of any two of the SQUIDs coupled to a single-mode cavity field. According to adjusting the level spacing, the entangled state of two SQUIDs can be realized in the case of large detuning and with the operation of classical pulse. With the same method, the GHZ and W entangled state of multi-SQUID can be achieved gradually. But the case is different in the second scheme, the GHZ and W entangled state is realized by the direct Raman coupling between the two lowest levels.