Distilling Nonlocality in Quantum Correlations

Nonlocality, as established by the seminal Bell's theorem, is considered to be the most striking feature of correlations present in spacelike separated events. Its practical application in device independent protocols, such as secure key distribution, randomness certification, etc., demands identification and amplification of such correlations observed in the quantum world. In this Letter we study the prospect of nonlocality distillation, wherein, by applying a natural set of free operations (called wirings) on many copies of weakly nonlocal systems, one aims to generate correlations of higher nonlocal strength. In the simplest Bell scenario, we identify a protocol, namely, logical OR-AND wiring, that can distill nonlocality to a significantly high degree starting from arbitrarily weak quantum nonlocal correlations. As it turns out, our protocol has several interesting facets: (i) it demonstrates that a set of distillable quantum correlations has nonzero measure in the full eight-dimensional correlation space, (ii) it can distill quantum Hardy correlations by preserving its structure, (iii) it shows that (nonlocal) quantum correlations sufficiently close to the local deterministic points can be distilled by a significant amount. Finally, we also demonstrate efficacy of the considered distillation protocol in detecting postquantum correlations.

Automated summary

This Letter examines the prospect of nonlocality distillation, wherein one aims to generate correlations of higher nonlocal strength by applying a natural set of free operations on many copies of weakly nonlocal systems. In the simplest Bell scenario, a protocol named logical OR-AND wiring is identified, which can distill nonlocality to a significantly high degree starting from arbitrarily weak quantum nonlocal correlations. The protocol demonstrates interesting facets, including the existence of a nonzero measure of distillable quantum correlations in the full eight-dimensional correlation space, the ability to distill quantum Hardy correlations by preserving its structure, and the distillation of (nonlocal) quantum correlations sufficiently close to the local deterministic points by a significant amount. The efficacy of the considered distillation protocol in detecting postquantum correlations is also demonstrated.