[Tian Gui-Hua] Beijing Univ Posts & Telecommun, Sch Sci, Beijing 100876, Peoples R China
; [Tian Gui-Hua] Chinese Acad Sci, Kavli Inst Theoret Phys China, Beijing 100190, Peoples R China
; [Zhong Shu-Quan] Beijing Univ Posts & Telecommun, State Key Lab Informat Photon & Opt Commun, Beijing 100876, Peoples R China
The entanglement of two qubits is investigated in the range of their ultra-strongly coupling with a quantum oscillator. The two qubits are initially in four Bell states and they are under the control mechanism of the coherent state of the quantum oscillator. There are four parameters: the average number of the coherent state, the ultra-strong coupling strength, the ratio of two frequencies of qubit and oscillator, and the inter-interaction coupling of the two qubits in the mechanism, and they all are influential parameters on the entanglement of the two qubits. One Bell state vertical bar I-0 > is easyily kept and is trivial case. The novel results show that there is one state vertical bar I-0 > among the other three Bell states which the entanglement of the two qubits could be almost completely preserved. The possibility is made into reality by the appropriate choice of the four influential parameters. We give two different schemes to choose the respective parameters to maintain the entanglment of vertical bar I-0 > almost undiminished. The results will be useful for the quantum information process.