Correlations are fundamental in describing many-body systems. However, in experiments, correlations are notoriously difficult to assess on a microscopic scale, especially for electron spins. Even though it is firmly established theoretically that the electrons in a Cooper pair¹ of a superconductor form maximally spin-entangled singlet states with opposite spin projections^2,3,4, no spin correlation experiments have been demonstrated so far. Here we report the direct measurement of the spin cross-correlations between the currents of a Cooper pair splitter^{5,6,7,8,9,10,11,12,13}, an electronic device that emits electrons originating from Cooper pairs. We use ferromagnetic split-gates^14,15, compatible with nearby superconducting structures, to individually spin polarize the transmissions of the quantum dots in the two electronic paths, which act as tunable spin filters. The signals are detected in standard transport and in highly sensitive transconductance experiments. We find that the spin cross-correlation is negative, consistent with spin singlet emission, and deviates from the ideal value mostly due to the overlap of the Zeeman split quantum dot states. Our results demonstrate a new route to perform spin correlation experiments in nano-electronic devices, especially suitable for those relying on magnetic field sensitive superconducting elements, like triplet or topologically non-trivial superconductors^16,17,18, or to perform Bell tests with massive particles^19,20.

相关性是描述多体系统的基础。然而，在实验中，众所周知，相关性很难在微观尺度上进行评估，尤其是对于电子自旋。尽管从理论上坚定地建立了超导体的库珀对^{1中的电子形成具有相反自旋投影2,3,4}的最大自旋纠缠单重态，但迄今为止尚未证明自旋相关实验。在这里，我们报告了库珀对分离器^{5,6,7,8,9,10,11,12,13}的电流之间的自旋互相关的直接测量，这是一种发射来自库珀对的电子的电子设备。我们使用铁磁分裂门^14,15，与附近的超导结构兼容，以单独自旋极化两条电子路径中量子点的传输，充当可调谐自旋滤波器。这些信号是在标准传输和高度敏感的跨导实验中检测到的。我们发现自旋互相关为负，与自旋单线态发射一致，并且偏离理想值主要是由于塞曼分裂量子点状态的重叠。我们的结果展示了在纳米电子设备中进行自旋相关实验的新途径，特别适用于那些依赖磁场敏感超导元件的设备，例如三重态或拓扑非平凡超导体^16,17,18，或使用大规模的贝尔测试颗粒^19,20。