Abstrakt
The correlations of multipartite quantum states have nonclassical features that go beyond entanglement. We analyze a hierarchy of quantumness measures for composite systems, defined in terms of the entanglement necessarily created between systems and apparata during local measurements. We prove that the quantumness so defined is always greater than intra-systems entanglement, establishing a firm ordering relation between different non-classical features of correlations. We analyze qualitatively and quantitatively the flow of correlations in iterated measurements, showing that quantumness and entanglement can never decrease along von Neumann chains. Our results provide a comprehensive framework to understand and quantify general signatures of quantumness in multipartite states, and shed light on quantum foundations and the quantum-to-classical transition.
