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

preprint

posted on 2023-01-11, 23:04 authored by Adetunmise C. Dada, Jędrzej Kaniewski, Corin Gawith, Martin Lavery, Robert H. Hadfield, Daniele Faccio, Matteo ClericiOwing 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.