Quantifying causal influences in the presence of a quantum common cause

Understand

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.