Quantum nonlocality revealed by local contextuality

Nicolas Gisin

Xiao‐Min Hu, Bi‐Heng Liu, Jiangshan Chen +5 more

Adán Cabello

Two distant systems can exhibit quantum nonlocality even though the correlations between them admit a local model. This nonlocality can be revealed by testing extra correlations between successive measurements on one of the systems which do not admit a noncontextual model whatever the reduced state of this system is. This shows that quantum contextuality plays a fundamental role in quantum nonlocality, and allows an experimental test of the Kochen-Specker with locality theorem.

Mary Bell, Shan Gao

Debashis Saha, Adán Cabello, Sujit K. Choudhary +1 more

Quantum nonlocality can be revealed ``via local contextuality'' in qudit-qudit entangled systems with $d>2$, that is, through the violation of inequalities containing Alice-Bob correlations that admit a local description, and Alice-Alice correlations (between the results of sequences of measurements on Alice's subsystem) that admit a local (but contextual) description. A fundamental question to understand the respective roles of entanglement and local contextuality is whether nonlocality via local contextuality exists when the parties have only qubit-qubit entanglement. Here we respond affirmatively to this question. This result further clarifies the connection between contextuality and nonlocality and opens the door for observing nonlocality via local contextuality in actual experiments.

Beatrix C. Hiesmayr, Jan-Åke Larsson

Everyday experience supports the existence of physical properties independent of observation in strong contrast to the predictions of quantum theory. In particular, the existence of physical properties that are independent of the measurement context is prohibited for certain quantum systems. This property is known as contextuality. This Rapid Communication studies whether the process of decay in space-time generally destroys the ability of revealing contextuality. We find that in the most general situation the decay property does not diminish this ability. However, applying certain constraints due to the space-time structure either on the time evolution of the decaying system or on the measurement procedure, the criteria revealing contextuality become inherently dependent on the decay property or an impossibility. In particular, we derive how the context-revealing setup known as Bell's nonlocality tests changes for decaying quantum systems. Our findings illustrate the interdependence between hidden and local hidden parameter theories and the role of time.