Can one see entanglement ?

TL;DR

This paper explores whether human eyes can serve as biological detectors to demonstrate quantum entanglement, showing that Bell inequalities can be violated with such detectors under certain conditions.

Contribution

It introduces a toy model for biological detectors like the human eye and demonstrates the possibility of observing quantum entanglement through them in Bell experiments.

Findings

Bell inequalities can be violated with biological detectors.

Quantum non-locality can be demonstrated without assumptions when response is step-like.

Post-selection is necessary for smoother detector response functions.

Abstract

The human eye can detect optical signals containing only a few photons. We investigate the possibility to demonstrate entanglement with such biological detectors. While one person could not detect entanglement by simply observing photons, we discuss the possibility for several observers to demonstrate entanglement in a Bell-type experiment, in which standard detectors are replaced by human eyes. Using a toy model for biological detectors that captures their main characteristic, namely a detection threshold, we show that Bell inequalities can be violated, thus demonstrating entanglement. Remarkably, when the response function of the detector is close to a step function, quantum non-locality can be demonstrated without any further assumptions. For smoother response functions, as for the human eye, post-selection is required.