Regarding the Maximal Qubit Violations of n-Locality in Star and Chain Networks

TL;DR

This paper derives larger, more noise-robust maximal n-local violations for star and chain quantum networks using previously overlooked observables, advancing understanding of nonlocal correlations in noisy quantum systems.

Contribution

It introduces new observables that lead to larger n-local violations in star and chain networks, improving robustness to noise and providing insights into self-testing and entanglement sources.

Findings

Larger n-local violations are achievable with new observables.

Violations are more robust to noise than previous results.

Provides insights into self-testing measurements in quantum networks.

Abstract

The nonlocal correlations of noisy quantum systems are important for both understanding nature and developing quantum technology. We consider the correlations of star and chain quantum networks where noisy entanglement sources are measured by nonsignaling parties. When pairs of local dichotomic observables are considered on qubit systems, we derive maximal n-local violations that are larger and more robust to noise than the maximal n-local violations reported previously. To obtain these larger values, we consider observables overlooked in the previous studies. Thus, we gain new insights into self-testing measurements and entanglement sources in star and chain networks.