Witnessing the Effective Entanglement in the COW Protocol

TL;DR

This paper develops a rigorous mathematical framework to verify effective entanglement in the COW quantum key distribution protocol, introducing new entanglement witnesses and analyzing experimental data.

Contribution

It introduces a two-parameter family of entanglement witnesses and demonstrates their effectiveness in revealing entanglement in the COW protocol.

Findings

Identification of valid parameter ranges for entanglement witnesses

Detection of effective entanglement in experimental COW data

Validation of the witnesses' ability to reveal entanglement

Abstract

We present a rigorous mathematical framework for verifying effective entanglement in a Coherent One-Way (COW) quantum key distribution setup. In particular, we introduce a two-parameter family of entanglement witnesses, identify the parameter ranges where they constitute valid witnesses, and demonstrate their ability to reveal effective entanglement in the COW protocol. Additionally, we analyze previously obtained experimental data from a COW implementation and report clear signatures of effective entanglement.