# Violation of the Bell-CHSH inequality and marginal laws in a single-entity Bell-test experiment

## TL;DR

This paper presents a simple experimental setup where a single entity can violate both Bell-CHSH inequality and marginal laws, challenging traditional notions of entanglement and nonlocality in quantum systems.

## Contribution

It demonstrates that violations of Bell-CHSH and marginal laws can occur in a single-entity context, providing new insights into the mechanisms behind such violations.

## Key findings

- Violations can occur with a single entity, not necessarily entangled bipartite systems.
- The choice of detection screens influences detection probabilities and violations.
- Bell-CHSH inequality can be violated up to its maximum value in this setup.

## Abstract

We describe a simple experimental setting where joint measurements performed on a single (classical or quantum) entity can violate both the Bell-CHSH inequality and the marginal laws (also called no-signaling conditions). Once emitted by a source, the entity propagates within the space of Alice's and Bob's detection screens, with the measurements' outcomes corresponding to the entity being absorbed or not absorbed in a given time interval. The violation of the marginal laws results from the fact that the choice of the screen on the side of Alice affects the detection probability on the side of Bob, and vice versa, and we show that for certain screen choices the Bell-CHSH inequality can be violated up to its mathematical maximum. Our analysis provides a clarification of the mechanisms that could be at play when the Bell-CHSH inequality and marginal laws are violated in entangled bipartite systems, which would not primarily depend on the presence of a bipartite structure but on the fact that the latter can manifest as an undivided whole.