The Schemes To Achieve Two Entangled States In Circuit QED

Quantum entanglement is considered to be the key resource in quantum information. At present,the schemes to prepare two-body entanglement in different systems have been proposed,in the meantime,tripartite or multipartite entanglement has been attracted broad attention too.The superconducting quantum computer which use the macroscopic state of superconducting Josephson junction device encoding information have been considered to be one of the most potential schemes to realize quantum computer for its great expansibility and it is easy to be controlled. The effective connection and interaction of superconducting qubits and SQUID constitute superconducting quantum circuit, various kinds of superconducting quantum circuit coupled with mecroscopic resonators(superconducting transmission line resonator, LC oscillator, nanomechanical resonator) can realize quantum logic gate and prepare entangled states and so on. In this paper, based on circuit QED we present several schemes to achieve entanglement states, mainly including the following aspects:1. We propose a scheme to achieve three-mode cv entanglement in circuit QED.2.We propose a simple scheme to prepare a four-qubit entangled cluster state in superconducting transmon qubit(STQ) system.