Bell nonlocality in the turbulent atmosphere

TL;DR

This paper investigates Bell inequality violations over turbulent atmospheric channels, finding that advantages of atmospheric links are limited to copropagation scenarios under strong loss fluctuations, with counterpropagation requiring additional postselection.

Contribution

The study reexamines Bell inequality violations in atmospheric channels, highlighting the limitations of atmospheric advantages in counterpropagation and proposing postselection to improve violations.

Findings

Atmospheric channels preserve Bell violations better in copropagation.

Counterpropagation benefits require channel transmittance postselection.

Strong loss fluctuations limit atmospheric advantages in Bell tests.

Abstract

Violations of Bell inequalities are better preserved by turbulent atmospheric channels than by comparable optical fibers in the scenario of copropagating entangled photons [A.A. Semenov and W. Vogel, Phys. Rev. A 81, 023835 (2010); arXiv:0909.2492]. Here we reexamine this result for the case of counterpropagation also considering the fact that each receiver registers so-called double-click events, which are caused by dark counts, stray light, and multi-photon entangled pairs. We show that advantages of the atmospheric links are feasible only for the copropagation scenario in the case of strong fluctuations of losses. For counterpropagation, the violations of Bell inequalities can be improved with an additional postselection procedure testing the channel transmittance.