Genuine hidden quantum nonlocality

TL;DR

This paper demonstrates the existence of genuine hidden quantum nonlocality in certain entangled states, revealing nonlocality only through sequences of measurements and maximal violations of Bell inequalities.

Contribution

It proves genuine hidden nonlocality for a class of two-qubit states, extending previous results to general measurements and showing maximal hidden nonlocality.

Findings

Existence of entangled states with genuine hidden nonlocality

Bell inequality violation after local filtering

Maximal hidden nonlocality achievable in some states

Abstract

The nonlocality of certain quantum states can be revealed by using local filters before performing a standard Bell test. This phenomenon, known as hidden nonlocality, has been so far demonstrated only for a restricted class of measurements, namely projective measurements. Here we prove the existence of genuine hidden nonlocality. Specifically, we present a class of two-qubit entangled states, for which we construct a local model for the most general local measurements (POVMs), and show that the states violate a Bell inequality after local filtering. Hence there exist entangled states, the nonlocality of which can be revealed only by using a sequence of measurements. Finally, we show that genuine hidden nonlocality can be maximal. There exist entangled states for which a sequence of measurements can lead to maximal violation of a Bell inequality, while the statistics of non-sequential measurements is always local.