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IEEE International Conference on Space Optical Systems and Applications (ICSOS)

CARAMUEL: The future of Space Quantum Key Distribution in GEO

Ángel Alvaro, Luis Pascual, Antonio Abad, Pedro Pinto, A. Álvarez‐Herrero, Tomás Belenguer, Carlos Miravet, Pablo Campo, Luis F. Rodriguez, Marcos Reyes, Jorge Socas, Javier Bermejo

Published Mar 28, 2022• 11 citations
Publisher

Abstract

The usage of QKD protocols through the current terrestrial infrastructure is limited to a hundred kilometers due to attenuation problems with fiber. This implies that the satellite will be necessary for the transmission of quantum keys in order to avoid these terrestrial limitations. Therefore, the current debate does not lie in the need for the satellite but rather in what type of infrastructure will be best suited, and specifically the usage of GEO vs LEO satellites. This analysis is not trivial and should not consider only the link budgets and the physical layer as it has been done up to date. It should also consider even more important factors, as the service KPIs that the end user will request such as key rate, availability, security of the keys and their maintenance, etc., as well as the possible communications architectures to provide the service. Therefore, the analysis should introduce the market oriented component, and provide the optimal solutions based on the scenarios and requirements requested by the customer. In this frame, and under ESA ARTES funding, a Spanish consortium led by Hispasat is defining an operational GEO QKD mission that shall fly as hosted payload in 2025. The quantum communications payload proposed in this mission represents a step beyond the state of the art since it is the first implementation of a quantum key distribution channel from geostationary orbit. This new service will involve the implementation of a complete communications system not currently available that will require the development of new technological elements and the adaptation for their operation in space of technologies such as photon sources, telescopes for optical communications compatible with quantum state transmission or processors for the distillation of quantum keys, as well as a whole new ground segment to control and manage the new quantum key distribution service and its integration into a future European secure quantum communications network. Details of the challenges and approach of this mission shall be presented

DOI
10.1109/icsos53063.2022.9749720

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The usage of QKD protocols through the current terrestrial infrastructure is limited to a hundred kilometers due to attenuation problems with fiber. This implies that the satellite will be necessary for the transmission of quantum keys in order to avoid these terrestrial limitations. Therefore, the current debate does not lie in the need for the satellite but rather in what type of infrastructure will be best suited, and specifically the usage of GEO vs LEO satellites. This analysis is not trivial and should not consider only the link budgets and the physical layer as it has been done up to date. It should also consider even more important factors, as the service KPIs that the end user will request such as key rate, availability, security of the keys and their maintenance, etc., as well as the possible communications architectures to provide the service. Therefore, the analysis should introduce the market oriented component, and provide the optimal solutions based on the scenarios and requirements requested by the customer. In this frame, and under ESA ARTES funding, a Spanish consortium led by Hispasat is defining an operational GEO QKD mission that shall fly as hosted payload in 2025. The quantum communications payload proposed in this mission represents a step beyond the state of the art since it is the first implementation of a quantum key distribution channel from geostationary orbit. This new service will involve the implementation of a complete communications system not currently available that will require the development of new technological elements and the adaptation for their operation in space of technologies such as photon sources, telescopes for optical communications compatible with quantum state transmission or processors for the distillation of quantum keys, as well as a whole new ground segment to control and manage the new quantum key distribution service and its integration into a future European secure quantum communications network. Details of the challenges and approach of this mission shall be presented
A feasibility study and the mission definition for a Quantum Key Distribution from a geostationary satellite have been successfully completed by a Spanish consortium led by HISPASAT under ARTES ESA funding. The system will be a hosted payload of a regular communication satellite mission. In this work, the conceptual optical design of the payload is presented. It includes the trade-off between an on-axis telescope with central obscuration and an off-axis unobscured telescope. Besides, the optical design of the transmission (i.e.: quantum signal and downlink beacon) and reception channels (i.e.: uplink beacon) are described and the critical subsystems identified. A polarization control system based on liquid-crystals, which avoids mechanisms, is used to correct the errors due to instrumental residual polarization, reference system rotation or long-term instability of the QKD source during operation.
Satellite based Quantum Key Distribution (QKD) systems appear as a potential solution to cover long distance links that cannot be satisfied through fiber links. In this frame, different alternatives are being evaluated involving both geostationary and low earth orbit. Most existing or planned space based QKD missions focus on the build, analysis and performance optimization of the physical quantum channel. This represents only a tiny part of the complexities that imply the design and operation of a commercial oriented full operational end to end QKD system. Based on the state of the art development of the future Spanish GEO QKD system, this paper covers a systemic approach to space based QKD systems, focusing on some limiting factors that need to be taken into account in order to achieve continuous operation of a QKD system from space. Systems parameters such as the on-board memory or the different system delays and their impact on continuous operation are studied. Finally, the paper presents how these different interactions have been arbitrated in the current design of the Spanish GEO QKD system that shall be built, launched and operated before 2030 with the support of the Spanish government and under EC funding.
Due to the distance limitation of quantum communication via ground-based fibre networks, space-based quantum key distribution (QKD) is a viable solution to extend such networks over continental and, ultimately, over global distances. Compared to LEO, QKD from GEO would offer substantial advantages, i.e. large coverage, continuous link to ground stations (cloud cover limited), 24/24h operation (background limited), no tracking required, however, coming with large link losses seen the space-ground distance. TNO, together with Eutelsat and CGI-NL, performed a detailed study on the feasibility of QKD from GEO, including a high level system design of payload and ground segment. We conclude that QKD from GEO is technically feasible, and a favourable solution if the satellite needs to act as an untrusted node (that is, no security assumptions required for the space segment). However, the optimal solution, generating a higher value-for-money, is to use a hybrid system, implementing an untrusted and trusted mode BBM92 QKD protocol. In order to arrive at a minimum required secure bit rate of ~1 bit/s in untrusted mode, a 2x ~0.5m diameter telescope in the space segment is required with <0.25µrad pointing accuracy, a <1GHz entangled photon source, in combination with ~2m diameter telescopes on ground. Details on our assumptions and results and drawings of the high level system design will be presented, as well as the development roadmap describing the required technology improvements and building blocks for the overall hybrid approach, which is applicable to non-GEO applications as well.
This paper presents the main architectural and technical elements of the Spanish initiative GARBO. This project, led by Thales Alenia Space Spain, with the support of Spanish authorities (CDTI), Operators (Hispasat) and other key industrial actors targets the definition, development, production and operation of a space based full end to end QKD system supported by a Prepare & Measure payload hosted and operated in a geostationary (GEO) telecommunications satellite. The target to operate from GEO orbit fixes strong constraints on the nature and operation of the system as will be shown in this paper. GARBO covers all R&D activities aimed at defining and demonstrating a complete quantum key transmission system (QKD) from geostationary orbit, to do so, as presented here, the GARBO team has designed the entire end-to-end system with special focus on the very stringent link budget for the quantum signal. Here, the optimal wavelength plan and has validated it through breadboard experiments. In the same way, both space and ground terminals are defined and presented. Finally, and being GARBO a project that targets full end to end operation, some overall system throughput analyses are drafted beyond the common Secure Key Rate figure directly linked to the QKD channel. Other higher level metrics and figures of merit are proposed to assess the adequacy of the proposed solution to the overall system needs and its potential integration with ground QKD networks such as the future EuroQCI.
We present a mission proposal to provide a space based quantum key distribution service. Using entangled photon pairs distributed to two ground stations with a simultaneous double downlink establishes a secret key directly at the user locations. The satellite and the payload do not generate or process any secret key information and the security design, certification and operation of the key management can be restricted to the user locations on ground. Positioning the satellite in GEO enables covering Europe and intercontinental connections, allows flexible service planning to cope with weather constraints and removes the need for coarse tracking telescopes in space and on ground while allowing long integration times. The large link distance and the combined losses of two down links require large optical terminals in space and on ground to obtain a usable secure key generation rate. We will present results from an ESA internal Phase 0 study concentrating on the payload design and performance.
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-based channels 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).