Quantum Key Distribution (QKD) is currently the only known technique that is able to guarantee information-theoretic secure communications. While many countries have already started developing use-cases based mostly on terrestrial links, the high losses that afflict fiber-basedchannels make them unsuitable for very-long-distance communications. Taking the quantum networks to a national and global scale thus requires the use of satellite-based quantum communications, as the attenuation experienced by photons in space communications is order of magnitudes lower than the one that characterizes terrestrial networks. Thales Alenia Space in Italy (TAS-I) is positioning itself as a key actor in the development of the technology needed to perform space quantum communications. In this work, we present an overview of the initiatives that are currently being carried out by TAS-I, and define a roadmap whose steps are planned to take the current laboratory experimentation towards the development of a fully operational QKD constellation meant to provide secret keys on a global scale. We also describe a possible implementation of an Italian demonstrator mission based on a LEO satellite that acts as a trusted node to distribute shared keys among a certain number of ground stations; we study the effects of some major system choices and assess the overall achievable performance in terms of Secret Key Volume (SKV).
Bob P. Dirks, Gustavo Castro do Amaral, David Bakker, Luca Mazzarella, Ivan Ferrario, Sander Kossen, Michiel Marcus, B. Perlingeiro Corrêa, Hemant Sharma, Alessandro Le Pera, Daniele Vito Finocchiaro, Martina Ottavi, Noemi Scaiella, Gabriele Riccardi
Quantum Key Distribution (QKD) is the most mature quantum technology, having achieved on-ground applications and commercially available products. In this domain, satellite platforms are essential to achieve a communication range reaching the intercontinental scale, acting thus as enablers for the future global quantum internet operation. This paper will report on the main results of the TNO-Eutelsat-TAS Italy project aiming to evaluate a novel hybrid approach for improved QKD performance particularly suited for geostationary orbits (GEO); the Dutch TKI HTSM sponsors the overall activity. We will present the results of lab-based tests of a novel QKD free-space approach that simultaneously implements the BBM92 protocol in both trusted and trust-free mode, following a joint Eutelsat-TNO patent. The trust-free mode between two ground receivers is the standard BBM92 protocol that uses entangled photons and there is no need for further security assumptions on the satellite payload. In trusted mode operation, one of the two entangled photons is measured directly on board. Key material is generated between ground and satellite. Security measures will be needed in the space segment, which therefore needs to be trusted. Further, we will present a demonstration roadmap aiming at free space field test to validate loss and key rate models for a free space link up to 2.5km in one of the arms. We also present a perspective on potential future GEO-based quantum applications beyond QKD. Additional presentation content can be accessed on the supplemental content page.
Future quantum networks offer the potential for new communication and computation applications. These quantum networks will undoubtedly require the routing of quantum information between distant parties. In order to reliably achieve the transmission of entangled states over such a network, some entanglement distillation protocol can be implemented on an ensemble of entangled photon pairs. Here, we demonstrate such a protocol by recovering quantum information using local filters on each photon of a polarization-entangled state in the presence of a common source of decoherence in the telecom fiber infrastructure, polarization mode dispersion (PMD).
We present a study of nonlocal polarization-mode dispersion (PMD) compensation in the framework of quantum information theory. We consider distribution of polarization-entangled photon pairs through optical fibers, where PMD acts as a decoherence mechanism. The use of additional controlled PMD in one of the two optical paths can restore the original degree of entanglement fully or in part, depending on the system configuration, in a nonlocal fashion. Using the quantum analog of the Shannon entropy, the Von Neumann entropy, we evaluate the quantum mutual information of propagated polarization-entangled photon pairs as a function of the fiber-channel PMD, and quantify the beneficial effect of nonlocal PMD compensation in terms of mutual quantum information restoration. All the relevant quantities can be extracted from the reduced density matrix characterizing the twophoton state polarization, which is obtained experimentally by means of customary polarization tomography.
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