We propose a unifying approach to the separability problem using covariance matrices of locally measurable observables. From a practical point of view, our approach leads to strong entanglement criteria that allow us to detect the entanglement of many bound entangled states in higher dimensions and which are at the same time necessary and sufficient for two qubits. From a fundamental perspective, our approach leads to insights into the relations between several known entanglement criteria—such as the computable cross-norm and local uncertainty criteria—as well as their limitations.

• Received 14 December 2006

DOI:https://doi.org/10.1103/PhysRevLett.99.130504