Stronger Quantum Correlations with Loophole-free Post-selection

TL;DR

This paper introduces a loophole-free post-selection method in multi-party Bell tests that can both close experimental loopholes and enhance quantum correlations, revealing new links between quantum non-classicality and computation.

Contribution

It presents a novel form of loophole-free post-selection that improves quantum correlations and connects non-classical correlations with non-classical computation.

Findings

Loophole-free post-selection can enhance quantum correlations.

The method provides a clearer operational framework for Bell tests.

It reveals a link between quantum non-classicality and computational power.

Abstract

One of the most striking non-classical features of quantum mechanics is in the correlations it predicts between spatially separated measurements. In local hidden variable theories, correlations are constrained by Bell inequalities, but quantum correlations violate these. However, experimental imperfections lead to "loopholes" whereby LHV correlations are no longer constrained by Bell inequalities, and violations can be described by LHV theories. For example, loopholes can emerge through selective detection of events. In this letter, we introduce a clean, operational picture of multi-party Bell tests, and show that there exists a non-trivial form of loophole-free post-selection. Surprisingly, the same post-selection can enhance quantum correlations, and unlock a connection between non-classical correlations and non-classical computation.