Near-maximal two-photon entanglement for quantum communications at 2.1 $\mu$m

TL;DR

This paper demonstrates near-maximally entangled photon pairs at 2.1 μm, a spectral region advantageous for daylight quantum communication, supporting potential device-independent quantum key distribution with high security.

Contribution

First demonstration of near-maximal entanglement at 2.1 μm supporting DIQKD, highlighting the spectral region's suitability for secure quantum communication.

Findings

Positive secure key rate of 0.254 bits per pair.

Quantum bit error rate of 3.8%.

Feasibility shown in laboratory conditions.

Abstract

Owing to a reduced solar background and low propagation losses in the atmosphere, the 2- to 2.5-$\mu$m waveband is a promising candidate for daylight quantum communication. This spectral region also offers low losses and low dispersion in hollow-core fibers and in silicon waveguides. We demonstrate for the first time near-maximally entangled photon pairs at 2.1 $\mu$m that could support device independent quantum key distribution (DIQKD) assuming sufficiently high channel efficiencies. The state corresponds to a positive secure-key rate (0.254 bits/pair, with a quantum bit error rate of 3.8%) based on measurements in a laboratory setting with minimal channel loss and transmission distance. This is promising for the future implementation of DIQKD at 2.1 $\mu$m.