Quantum mechanics challenges our intuition on the cause-effect relations in nature. Some fundamental concepts, including Reichenbach’s common cause principle or the notion of local realism, have to be reconsidered. Traditionally, this is witnessed by the violation of a Bell inequality. But are Bell inequalities the only signature of the incompatibility between quantum correlations and causality theory? Motivated by this question we introduce a general framework able to estimate causal influences between two variables, without the need of interventions and irrespectively of the classical, quantum, or even post-quantum nature of a common cause. In particular, by considering the simplest instrumental scenario -for which violation of Bell inequalities is not possible- we show that every pure bipartite entangled state violates the classical bounds on causal influence, thus answering in negative to the posed question and opening a new venue to explore the role of causality within quantum theory.

中文翻译：

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在存在量子共同原因的情况下量化因果影响

量子力学挑战了我们对自然中因果关系的直觉。必须重新考虑一些基本概念，包括赖兴巴赫的“共同因果原则”或局部现实主义概念。传统上，这是通过违反贝尔不等式来证明的。但是，贝尔不等式是量子相关性与因果理论之间不相容性的唯一标志吗？出于这个问题的动机，我们引入了一个通用框架，该框架能够估计两个变量之间的因果影响，而无需干预，并且与常见原因的经典，量子或什至量子后性质无关。尤其是，