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arXiv quant-ph/0004109quant-ph
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隐藏变量还是正概率?

Hidden Variables or Positive Probabilities?

Tony Rothman, E. C. G. Sudarshan

摘要:

尽管声称贝尔不等式是基于爱因斯坦定域性条件或等价条件,但所有的推导都有一个相同的数学假设:定域隐变量理论产生一组正定概率来检测具有给定自旋方向的粒子。标准的论点是,因为量子力学假设粒子是以叠加态发射的,所以理论不能产生这样一组概率。我们研究了Eberhard的一篇论文,以及几篇类似的论文,它们声称证明了一个广义的贝尔不等式,CHSH不等式,可以仅仅根据局部性条件导出,而不需要借助于隐变量。我们指出,尽管如此,这些作者假设了一组正定概率,这支持了这样一种说法,即隐变量或“局部性”在这里不是问题,正定概率是。我们证明了量子力学确实预言了一组违反CHSH不等式的概率,但是这些概率不是正定的。然而,它们在物理上是有意义的,因为它们给出了物理情况下通常的量子力学预测。我们讨论在什么意义上我们的结果是相关的维格纳分布。

英文摘要:

Despite claims that Bell's inequalities are based on the Einstein locality condition, or equivalent, all derivations make an identical mathematical assumption: that local hidden-variable theories produce a set of positive-definite probabilities for detecting a particle with a given spin orientation. The standard argument is that because quantum mechanics assumes that particles are emitted in a superposition of states the theory cannot produce such a set of probabilities. We examine a paper by Eberhard, and several similar papers, which claim to show that a generalized Bell inequality, the CHSH inequality, can be derived solely on the basis of the locality condition, without recourse to hidden variables. We point out that these authors nonetheless assumes a set of positive-definite probabilities, which supports the claim that hidden variables or "locality" is not at issue here, positive-definite probabilities are. We demonstrate that quantum mechanics does predict a set of probabilities that violate the CHSH inequality; however these probabilities are not positive-definite. Nevertheless, they are physically meaningful in that they give the usual quantum-mechanical predictions in physical situations. We discuss in what sense our results are related to the Wigner distribution.

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