约瑟夫森结量子特性的再研究
Quantumness of Josephson junctions reexamined
摘要：
越来越多的证据支持约瑟夫森结（JJ）是一个“宏观量子系统”。另一方面，实验数据的解释强烈依赖于假设的理论模型。我们分析了两种模型下库珀对盒（“电荷量子比特”）的可能状态：双模Bose-哈伯德模型及其大$N$近似和平均场近似下的多体描述（Gross-Pitaevski方程）。虽然第一类模型支持的图片JJ是一个量子子系统的一个单一的自由度，第二种方法产生一个基本上经典的结构，可访问的量子态，特别是，这意味着没有纠缠的两个耦合JJ的。赞成的平均场论的论点和不同的实验测试，包括一个新的建议进行了简要讨论。
英文摘要：
There exists an increasing evidence supporting the picture of the Josephson junction (JJ) as a "macroscopic quantum system". On the other hand the interpretation of experimental data strongly depends on the assumed theoretical model. We analyse the possible states of a Cooper pair box ("charge qubit") for the two types of models : two-mode Bose-Hubbard model with its large $N$ aproximations and the many-body description within the mean-field approximation (Gross-Pitaevski equation). While the first class of models supports the picture of JJ being a quantum subsystem of a single degree of freedom, the second approach yields an essentially classical structure of accessible quantum states which, in particular, implies the absence of entanglement for two coupled JJ's. The arguments in favor of the mean-field theory are presented and different experimental tests including a new proposal are briefly discussed.
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