title: A subsystem-independent generalization of entanglement.
abstract: We present a generalization of entanglement based on the idea that entanglement is relative to a distinguished subspace of observables rather than a distinguished subsystem decomposition. A pure quantum state is entangled relative to such a subspace if its expectations are a proper mixture of those of other states. Many information-theoretic aspects of entanglement can be extended to this observable-based setting, suggesting new ways of measuring and classifying multipartite entanglement. By going beyond the distinguishable-subsystem framework, generalized entanglement also provides novel tools for probing quantum correlations in interacting many-body systems.
authors.affiliation: Los Alamos National Laboratory, MS B256, Los Alamos, New Mexico 87545, USA.
authors.forename: Howard
authors.initials: H
authors.lastname: Barnum
authors.forename: Emanuel
authors.initials: E
authors.lastname: Knill
authors.forename: Gerardo
authors.initials: G
authors.lastname: Ortiz
authors.forename: Rolando
authors.initials: R
authors.lastname: Somma
authors.forename: Lorenza
authors.initials: L
authors.lastname: Viola