Quantum versus classical entanglement: eliminating the issue of quantum nonlocality

TL;DR

This paper examines the relationship between quantum and classical entanglement, challenging the idea that quantum nonlocality is the key difference, and highlights the importance of the 1986 Grangier experiment in distinguishing quantum from classical light.

Contribution

It clarifies the distinction between quantum and classical entanglement by analyzing experimental and theoretical aspects, emphasizing the role of the 1986 experiment and the measurement techniques.

Findings

Classical entanglement can mimic some quantum features but differs in coherence properties.

The 1986 Grangier experiment was pivotal in rejecting classical field models.

Measurement methods influence the interpretation of entanglement phenomena.

Abstract

We analyze interrelation of quantum and classical entanglement. The latter notion is widely used in classical optic simulation of some quantum-like features of light. We criticize the common interpretation that "quantum nonlocality" is the basic factor differing quantum and classical realizations of entanglement. Instead, we point to the breakthrough Grangier et al. experiment on coincidence detection which was done in 1986 and played the crucial role in rejection of (semi-)classical field models in favor of quantum mechanics. Classical entanglement sources produce light beams with the coefficient of second order coherence $g^{(2)}(0) \geq 1.$ This feature of classical entanglement is obscured by using intensities of signals in different channels, instead of counting clicks of photo-detectors. Interplay between intensity and clicks counting is not just a technicality. We elevate this issue to the high foundational level.