# Quantum observation scheme universally identifying causalities from correlations

## TL;DR

This paper introduces a universal quantum observation scheme that can distinguish between quantum causality and quantum common causes in all cases, advancing the understanding of quantum causal inference.

## Contribution

It proves that quantum common causes and quantum causality are universally separable and provides a general method for their discrimination.

## Key findings

- Quantum common causes and quantum causality are universally separable.
- A general method for distinguishing quantum causality from common causes is proposed.
- The approach applies to all cases, overcoming previous limitations.

## Abstract

It has long been recognized as a difficult problem to determine whether the observed statistical correlation between two classical variables arise from causality or from common causes. Recent research has shown that in quantum theoretical framework, the mechanisms of entanglement and quantum coherence provide an advantage in tackling this problem. In some particular cases, quantum common causes and quantum causality can be effectively distinguished using observations only. However, these solutions do not apply to all cases. There still exist enormous cases in which quantum common causes and quantum causality can not be distinguished. In this paper, along the line of considering unitary transformation as causality in the quantum world, we formally show quantum common causes and quantum causality are universally separable. Based on the analysis, we further provide a general method to discriminate the two.