Multi-user distribution of polarization entangled photon pairs

TL;DR

This paper demonstrates the practical distribution of polarization-entangled photon pairs to multiple users using commercial wavelength division demultiplexers, showing Bell inequality violations over significant distances for quantum communication networks.

Contribution

It introduces a method for multi-user entanglement distribution using commercial demultiplexers and analyzes their impact on entanglement quality, advancing quantum network implementations.

Findings

Bell inequality violation achieved for three user pairs

Entanglement maintained over 20 km fiber equivalent distance

Demonstrated compatibility with practical quantum communication setups

Abstract

We experimentally demonstrate multi-user distribution of polarization entanglement using commercial tele- com wavelength division demultiplexers. The entangled photon pairs are generated from a broadband source based on spontaneous parametric down conversion in a periodically poled lithium niobate crystal using a double path setup employing a Michelson interferometer and active phase stabilisation. We test and compare demultiplexers based on various technologies and analyze the effect of their characteristics, such as losses and polarization dependence, on the quality of the distributed entanglement for three channel pairs of each demultiplexer. In all cases, we obtain a Bell inequality violation, whose value depends on the demultiplexer features. This demonstrates that entanglement can be distributed to at least three user pairs of a network from a single source. Additionally, we verify for the best demultiplexer that the violation is maintained when the pairs are distributed over a total channel attenuation corresponding to 20 km of optical fiber. These tech- niques are therefore suitable for resource-efficient practical implementations of entanglement-based quantum key distribution and other quantum communication network applications.