Bell tests with random measurements require very high detection efficiencies

TL;DR

This paper demonstrates that violating Bell inequalities with random measurements requires very high detection efficiencies, revealing that detection efficiency is a critical resource for practical quantum nonlocality demonstrations.

Contribution

The study shows that high detection efficiency (above 0.90) is essential for Bell tests with random measurements, challenging previous assumptions about their robustness.

Findings

Violation probability drops below 0.02% at 78.5% efficiency

Detection efficiency is more crucial than previously believed

High detection efficiency is necessary for real-world Bell tests

Abstract

The observation that violating Bell inequalities with high probability is possible even when the local measurements are randomly chosen, as occurs when local measurements cannot be suitably calibrated or the parties do not share a common reference frame, has recently attracted much theoretical and experimental efforts. Here we show that this observation is only valid when the overall detection efficiency is very high ($\eta \geq 0.90$), otherwise, even when using the highest detection efficiency of recent photonic Bell tests, the probability of demonstrating nonlocality is negligible (e.g., it is smaller than 0.02% for $\eta=0.785$). Our results show that detection efficiency is a much more critical resource for real-world applications than it was previously thought.