Distilling Nonlocality in Quantum Correlations

TL;DR

This paper presents a protocol for distilling stronger nonlocal quantum correlations from weaker ones using wirings, with implications for quantum information tasks and detection of postquantum correlations.

Contribution

It introduces a logical OR-AND wiring protocol that effectively distills nonlocality, revealing the non-zero measure of distillable quantum correlations and its ability to preserve Hardy correlations.

Findings

Distillation protocol significantly increases nonlocality from weak correlations.

The set of distillable quantum correlations has non-zero measure.

Protocol can detect postquantum correlations.

Abstract

Nonlocality, as established by seminal Bell's theorem, is considered to be the most striking feature of correlations present in space like separated events. Its practical application in device independent protocols, such as secure key distribution, randomness certification, {\it 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 distil nonlocality to significantly high degree starting from arbitrarily weak quantum nonlocal correlations. As it turns out, our protocol has several interesting facets: (i) it demonstrates that set of distillable quantum correlations has non zero measure in the full eight-dimensional correlation space, (ii) it can distil 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.