Two-photon quantum interference and entanglement at 2.1 μm

Prabhakar, Shashi and Shields, Taylor and Dada, Adetunmise C. and Ebrahim, Mehdi and Taylor, Gregor G. and Morozov, Dmitry and Erotokritou, Kleanthis and Miki, Shigehito and Yabuno, Masahiro and Terai, Hirotaka and Gawith, Corin and Kues, Michael and Caspani, Lucia and Hadfield, Robert H. and Clerici, Matteo (2020) Two-photon quantum interference and entanglement at 2.1 μm. Science Advances, 6 (13). eaay5195. ISSN 2375-2548

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    Quantum-enhanced optical systems operating within the 2- to 2.5-μm spectral region have the potential to revolutionize emerging applications in communications, sensing, and metrology. However, to date, sources of entangled photons have been realized mainly in the near-infrared 700- to 1550-nm spectral window. Here, using custom-designed lithium niobate crystals for spontaneous parametric down-conversion and tailored superconducting nanowire single-photon detectors, we demonstrate two-photon interference and polarization-entangled photon pairs at 2090 nm. These results open the 2- to 2.5-μm mid-infrared window for the development of optical quantum technologies such as quantum key distribution in next-generation mid-infrared fiber communication systems and future Earth-to-satellite communications.