title: Quantum networks reveal quantum nonlocality.
abstract: The results of local measurements on some composite quantum systems cannot be reproduced classically. This impossibility, known as quantum nonlocality, represents a milestone in the foundations of quantum theory. Quantum nonlocality is also a valuable resource for information-processing tasks, for example, quantum communication, quantum key distribution, quantum state estimation or randomness extraction. Still, deciding whether a quantum state is nonlocal remains a challenging problem. Here, we introduce a novel approach to this question: we study the nonlocal properties of quantum states when distributed and measured in networks. We show, using our framework, how any one-way entanglement distillable state leads to nonlocal correlations and prove that quantum nonlocality is a non-additive resource, which can be activated. There exist states, local at the single-copy level, that become nonlocal when taking several copies of them. Our results imply that the nonlocality of quantum states strongly depends on the measurement context.
authors.affiliation: Centre for Quantum Technologies, National University of Singapore, Singapore 117542, Singapore. dcavalcanti@gmail.com
authors.forename: Daniel
authors.initials: D
authors.lastname: Cavalcanti
authors.forename: Mafalda L
authors.initials: ML
authors.lastname: Almeida
authors.forename: Valerio
authors.initials: V
authors.lastname: Scarani
authors.forename: Antonio
authors.initials: A
authors.lastname: Acín
mesh_terms: D001330:Electronic Data Processing / Q000379:methods*; D008962:Models, Theoretical; D011789:Quantum Theory