Hasegawa Yuji, Loidl Rudolf, Badurek Gerald, Baron Matthias, Rauch Helmut
Atominstitut der Osterreichischen Universitäten, Stadionallee 2, A-1020 Wien, Austria.
Nature. 2003 Sep 4;425(6953):45-8. doi: 10.1038/nature01881.
Non-local correlations between spatially separated systems have been extensively discussed in the context of the Einstein, Podolsky and Rosen (EPR) paradox and Bell's inequalities. Many proposals and experiments designed to test hidden variable theories and the violation of Bell's inequalities have been reported; usually, these involve correlated photons, although recently an experiment was performed with (9)Be(+) ions. Nevertheless, it is of considerable interest to show that such correlations (arising from quantum mechanical entanglement) are not simply a peculiarity of photons. Here we measure correlations between two degrees of freedom (comprising spatial and spin components) of single neutrons; this removes the need for a source of entangled neutron pairs, which would present a considerable technical challenge. A Bell-like inequality is introduced to clarify the correlations that can arise between observables of otherwise independent degrees of freedom. We demonstrate the violation of this Bell-like inequality: our measured value is 2.051 +/- 0.019, clearly above the value of 2 predicted by classical hidden variable theories.
在爱因斯坦 - 波多尔斯基 - 罗森（EPR）悖论和贝尔不等式的背景下，空间分离系统之间的非局域关联已得到广泛讨论。已经报道了许多旨在检验隐变量理论和贝尔不等式违背情况的提议和实验；通常，这些实验涉及相关光子，不过最近有一个使用（9）Be（+）离子进行的实验。然而，证明这种（源于量子力学纠缠的）关联并非光子所特有的性质是相当有趣的。在这里，我们测量单个中子的两个自由度（包括空间和自旋分量）之间的关联；这消除了对纠缠中子对源的需求，而纠缠中子对源会带来相当大的技术挑战。引入了一个类似贝尔的不等式来阐明在其他方面独立的自由度的可观测量之间可能出现的关联。我们证明了对这个类似贝尔不等式的违背：我们测量的值为2.051±0.019，明显高于经典隐变量理论预测的2值。
