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Proceedings Paper

Stratospheric QKD: feasibility analysis and free-space optics system concept
Author(s): Florian Moll; Thierry Botter; Christoph Marquardt; David Pusey; Amita Shrestha; Andrew Reeves; Kevin Jaksch; Kevin Gunthner; Oemer Bayraktar; Christian Mueller-Hirschkorn; Alberto Diago Gallardo; Dionisio Diaz Gonzalez; Wenjamin Rosenfeld; Peter Freiwang; Gerd Leuchs; Harald Weinfurter
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Paper Abstract

Quantum key distribution (QKD) is one of the most mature quantum technologies and can provide quantum-safe security in future communication networks. Since QKD in fiber is limited to a range of few hundred kilometers, one approach to bridge continental scale distances may be the use of high altitude pseudo satellites (HAPS) as mobile trusted nodes in the stratosphere. In parallel, free-space laser communication for high rate data transmission has been a subject of research and development for several decades and its commercialization is progressing rapidly. Important synergies exist between classical free-space communication and QKD systems since the quantum states are often implemented using the same degrees of freedom such as polarization or field amplitude and phase. These synergies can be used to benefit from the progress in classical free-space laser communication in QKD applications. In this paper, the use case of QKD in a stratospheric environment is described wherein HAPS may serve as relay station of secret keys and encrypted data. The mission scenario and HAPS capabilities are analyzed to derive special requirements on the stratospheric laser terminal, the link geometry and the ground segment with respect to a feasibility demonstration. To obtain a flexible and compatible system, discrete variable and continuous variable QKD protocols are considered to be implemented side by side in the HAPS payload. Depending on the system parameters, it can be beneficial to use the one or the other kind of protocol. Thus, a direct comparison of both in one and the same system is of scientific interest. Each of the protocols has particular requirements on coupling efficiency and implementation. Link budget calculations are performed to analyze possible distances, key rates and data transmission rates for the different schemes. In case of the QKD system, the mean coupling efficiency is of main interest, i.e. signal fluctuations arising from atmospheric turbulence must be taken into account in the security proof, but the buffered key generation relaxes real-time requirements. This is different to classical communications, where the corresponding fading loss must be assessed. A system architecture is presented that comprises the optical aircraft terminal, the optical ground terminal and the most important subsystems that enable implementation of the considered QKD protocols. The aircraft terminal is interfaced with the dedicated quantum transmitter module (Alice) and the ground station with the dedicated quantum receiver module (Bob). The optical interfaces are SMF couplings which put high requirements on the receiving optics, in particular the need for wave-front correction with adaptive optics. The findings of the system study are reviewed and necessary next steps pointed out.

Paper Details

Date Published: 7 October 2019
PDF: 9 pages
Proc. SPIE 11167, Quantum Technologies and Quantum Information Science V, 111670H (7 October 2019); doi: 10.1117/12.2539076
Show Author Affiliations
Florian Moll, Deutsches Zentrum für Luft- und Raumfahrt e.V. (Germany)
Thierry Botter, Airbus Defence and Space GmbH (Germany)
Christoph Marquardt, Max-Planck-Institut für die Physik des Lichts (Germany)
David Pusey, Airbus Defence and Space GmbH (United Kingdom)
Amita Shrestha, Deutsches Zentrum für Luft- und Raumfahrt e.V. (Germany)
Andrew Reeves, Deutsches Zentrum für Luft- und Raumfahrt e.V. (Germany)
Kevin Jaksch, Max-Planck-Institut für die Physik des Lichts (Germany)
Kevin Gunthner, Max-Planck-Institut für die Physik des Lichts (Germany)
Oemer Bayraktar, Max-Planck-Institut für die Physik des Lichts (Germany)
Christian Mueller-Hirschkorn, Max-Planck-Institut für die Physik des Lichts (Germany)
Alberto Diago Gallardo, Mynaric Lasercom GmbH (Germany)
Dionisio Diaz Gonzalez, Mynaric Lasercom GmbH (Germany)
Wenjamin Rosenfeld, Ludwig-Maximilians-Univ. München (Germany)
Peter Freiwang, Ludwig-Maximilians-Univ. München (Germany)
Gerd Leuchs, Max-Planck-Institut für die Physik des Lichts (Germany)
Harald Weinfurter, Ludwig-Maximilians-Univ. München (Germany)

Published in SPIE Proceedings Vol. 11167:
Quantum Technologies and Quantum Information Science V
Mark T. Gruneisen; Miloslav Dusek; Paul M. Alsing; John G. Rarity, Editor(s)

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