When More Light Means Less Quantum: Modeling Bell Inequality Degradation from Accidental Counts

TL;DR

This paper models how accidental counts from false detection events reduce Bell inequality violations in photonic experiments, providing a practical tool to optimize quantum source brightness for secure quantum technologies.

Contribution

It introduces a simple noise model that quantitatively relates pump power to Bell violation degradation, validated with experimental data.

Findings

Bell violations decrease with increased pump power due to accidental counts.

The model accurately predicts Bell values across different pump settings.

Guidelines for optimizing source brightness to maintain quantum nonlocality.

Abstract

We investigate how accidental counts, the detection events not originating from genuine entangled photon pairs, impact the observed violation of Bell inequalities in photonic experiments. These false coincidences become increasingly significant at higher laser pump powers, limiting the strength of Bell violations and thus the performance of quantum protocols such as device-independent quantum random number generation and quantum key distribution. We propose a simple noise model that quantitatively links the Bell value to the pump strength. Using experimental data from recent SPDC-based Bell tests, we fit the model to a Bell expression, and demonstrate accurate prediction of Bell values across a range of pump settings. Our results provide practical guidance for optimizing source brightness while preserving quantum nonlocality, with direct implications for high-rate, secure quantum technologies.