Quantum Atom Optics Laboratory, Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543. Quantum Optics Theory Group, Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Science. 2016 Apr 22;352(6284):441-4. doi: 10.1126/science.aad8665.
Characterizing many-body systems through the quantum correlations between their constituent particles is a major goal of quantum physics. Although entanglement is routinely observed in many systems, we report here the detection of stronger correlations--Bell correlations--between the spins of about 480 atoms in a Bose-Einstein condensate. We derive a Bell correlation witness from a many-particle Bell inequality involving only one- and two-body correlation functions. Our measurement on a spin-squeezed state exceeds the threshold for Bell correlations by 3.8 standard deviations. Our work shows that the strongest possible nonclassical correlations are experimentally accessible in many-body systems and that they can be revealed by collective measurements.
通过研究组成它们的粒子之间的量子相关性来描述多体系统是量子物理学的主要目标。尽管在许多系统中都可以观察到纠缠，但我们在这里报告了在玻色-爱因斯坦凝聚体中的约 480 个原子的自旋之间检测到更强的相关性——贝尔相关性。我们从一个只涉及单粒子和双粒子相关函数的多粒子贝尔不等式中推导出了一个贝尔相关的见证。我们对自旋压缩态的测量超过了贝尔相关性的阈值 3.8 个标准差。我们的工作表明，在多体系统中可以实验上获得最强的可能非经典相关性，并且可以通过集体测量来揭示它们。
