# Experimental many-pairs nonlocality

## TL;DR

This paper investigates how different measurement binning strategies affect Bell inequality violations in large quantum systems, demonstrating nonlocal correlations with over 40 photon pairs and proposing a method to quantify source quality.

## Contribution

It introduces a novel binning strategy that enhances Bell violations in multi-pair quantum systems under low noise conditions and uses this to assess photon source quality.

## Key findings

- A new binning strategy improves Bell violation magnitude.
- Nonlocal correlations observed with clusters of over 40 photon pairs.
- Critical pair number correlates with source noise levels.

## Abstract

Collective measurements on large quantum systems together with a majority voting strategy can lead to a violation of the CHSH Bell inequality. In presence of many entangled pairs, this violation decreases quickly with the number of pairs, and vanishes for some critical pair number that is a function of the noise present in the system. Here, we show that a different binning strategy can lead to a more substantial Bell violation when the noise is sufficiently small. Given the relation between the critical pair number and the source noise, we then present an experiment where the critical pair number is used to quantify the quality of a high visibility photon pair source. Our results demonstrate nonlocal correlations using collective measurements operating on clusters of more than 40 photon pairs.