The transfer of the quantum correlation from two-mode nonclassical state field to the supercurrents in two distant SQUID rings
Peng Zhao-Hui(彭朝辉)a)b), Zou Jian(邹健)a)†, and Shao Bin(邵彬)a)
a Department of Physics, Beijing Institute of Technology, Beijing 100081, China; b Department of Physics, Beijing Institute of Technology, Beijing 100081, China;Department of Physics, Hunan University of Science and Technology, Xiangtan 411201, China
Abstract We have considered two distant mesoscopic superconducting quantum interference device (SQUID) rings A and B in the presence of two-mode nonclassical state fields and investigated the correlation of the supercurrents in the two rings using the normalized correlation function $C_{\rm AB}$. We show that when the parameter $\alpha$ is very small for the separable state with the density matrix $\hat {\rho } = (\left| {\alpha , - \alpha } \right\rangle \left\langle {\alpha , - \alpha } \right| + \left| { - \alpha ,\alpha } \right\rangle \left\langle { - \alpha ,\alpha } \right|) / 2$ and entangled coherent state (ECS) $\left| u \right\rangle = N_1 (\left| {\alpha , - \alpha } \right\rangle + \left| { - \alpha ,\alpha } \right\rangle )$ fields, the dynamic behaviours of the normalized correlation function $C_{\rm AB}$ are similar, but it is quite different for the entangled coherent state $\left| {u}' \right\rangle = N_2 (\left| {\alpha , - \alpha } \right\rangle - \left| { - \alpha ,\alpha } \right\rangle )$ field. When the parameter $\alpha $ is very large, the dynamic behaviours of $C_{\rm AB}$ are almost the same for the separable state, entangled coherent state $\left| u \right\rangle $ and $\left| {u}' \right\rangle $ fields. For the two-mode squeezed vacuum state field the maximum of $C_{\rm AB}$ increases monotonically with the squeezing parameter $r$, and as $r \to \infty $, $C_{\rm AB} \to 1$. This means that the supercurrents in the two rings A and B are quantum mechanically correlated perfectly. It is concluded that not all the quantum correlations in the two-mode nonclassical state field can be transferred to the supercurrents; and the transfer depends on the state of the two-mode nonclassical state field prepared.
Received: 07 May 2006
Revised: 14 March 2007
Accepted manuscript online:
Fund: Project supported by the
National Natural Science Foundation of China (Grant No
10374007).
Cite this article:
Peng Zhao-Hui(彭朝辉), Zou Jian(邹健), and Shao Bin(邵彬) The transfer of the quantum correlation from two-mode nonclassical state field to the supercurrents in two distant SQUID rings 2007 Chinese Physics 16 2569
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