High-dimensional intracity quantum cryptography with structured photons

• DOI: 10.1364/optica.4.001006
• Publication Date: 2017-08-24T13:11:07Z
• Authors: Alicia Sit; Frédéric Bouchard; Robert Fickler; Jérémie Gagnon-Bi...; Hugo Larocque; Khabat Heshami; Dominique Elser; Christian Peuntinger; Kevin Günthner; Bettina Heim; Christoph Marquardt; Gerd Leuchs; Robert W. Boyd; Ebrahim Karimi
• Keywords: Quantum key distribution; BB84

Quantum key distribution (QKD) promises information-theoretically secure communication, and is already on the verge of commercialization. Thus far, different QKD protocols have been proposed theoretically implemented experimentally [1, 2]. The next step will be to implement high-dimensional in order improve noise resistance increase data rate [3-7]. Hitherto, no experimental verification single-photon regime has conducted outside laboratory. Here, we report realization such a system turbulent free-space link 0.3 km over city Ottawa, taking advantage both spin orbital angular momentum photonic degrees freedom. This combination optical momenta allows us create 4-dimensional state [8]; wherein, using BB84 protocol [3, 4], quantum bit error 11\% was attained with corresponding secret 0.65 bits per sifted photon. While an 5\% 0.43 photon achieved for case 2-dimensional structured photons. Even through moderate turbulence without active wavefront correction, it possible securely transmit information carried by photons, opening way intra-city communications under realistic conditions.