On the brink of the so-called quantum age, researchers from around the globe go to great lengths to better understand the quantum nature of light. Browne et al. (2017, p.1) state: 'Quantum light remains at the heart of many of the most promising and potentially transformative quantum technologies'. With the huge progress in quantum computing over the last years, quantum key distribution (QKD) is equally growing in importance. By exchanging secure keys using an optical link, QKD is able to solve security vulnerabilities arising through the insufficient protection of traditional encryption techniques against brute force quantum computer attacks threatening future communications. Pushing the limits of optical free space links for many years, the German Aerospace Center (DLR) has also gathered a lot of experience in QKD applications and is now aiming for a safe and powerful future optical communication network. As QKD networks become reality, optical freespace links ensure ground-satellite and satellite-satellite communication lines. Essential for ground-satellite links are accurate telescopes, which reduce satellite optics requirements due to their ability to gather light and focus collimated beams.
On the brink of the so-called quantum age, researchers from around the globe go to great lengths to better understand the quantum nature of light. Browne et al. (2017, p.1) state: 'Quantum light remains at the heart of many of the most promising and potentially transformative quantum technologies'. With the huge progress in quantum computing over the last years, quantum key distribution (QKD) is equally growing in importance. By exchanging secure keys using an optical link, QKD is able to solve security vulnerabilities arising through the insufficient protection of traditional encryption techniques against brute force quantum computer attacks threatening future communications. Pushing the limits of optical free space links for many years, the German Aerospace Center (DLR) has also gathered a lot of experience in QKD applications and is now aiming for a safe and powerful future optical communication network. As QKD networks become reality, optical freespace links ensure ground-satellite and satellite-satellite communication lines. Essential for ground-satellite links are accurate telescopes, which reduce satellite optics requirements due to their ability to gather light and focus collimated beams.
Laser communication technology, especially QKD (Quantum Key Distribution), is coming more and more into practical operations. It is a maturing technology that enables the distribution of cryptographic key between two remote parties [1][3] for secure communication even in presence of quantum computers[3]. To demonstrate this technology DLR is part of the QUBE project to have a precursor mission for QKD from CubeSats in orbit as well as hosting and operating the ground-based counterpart the Optical Ground Station Oberpfaffenhofen (OGSOP).The OGS is equipped with an 80cm primary mirror, a Coudé path with optical bench, adaptive optics system, fiber coupling and a single photon detector. The ground station already performed successful downlinks from low Earth orbit (LEO) (Flying Laptop, CubeL and others) and geostationary platforms (Alphasat, Project BayernQSat), as well as aircrafts (Project QuNET) [4][11][13].In the last year the ground station was upgraded from its basic configuration to adapt for multi-mission support and QKD experiments. Several features were integrated and upgraded at the telescope, in the Coudé path and on the optical bench. The focus of the upgrades was to connect the OGSOP (Optical Ground Station Oberpfaffenhofen) with the satellite QUBE. The target of compatibility could be achieved and improved from OGS side.Knowledge from ground-to-ground-tests were considered to rebuild the receiving setups in an improved and more operational way. The QUBE satellite contains an optical terminal designed and developed by DLR to transmit two experimental quantum signals over the optical link. These sources were developed by the Ludwig-Maximilian University (LMU) of Munich and the Friedrich-Alexander University (FAU) in Erlangen.On May the 2nd 2025 the OGSOP was able to catch the first light from QUBE and establish a link between both sides[2]. This started the optical communication commissioning phase of the satellite, including the classical communication terminal and the quantum light sources. This paper describes the entire setup, from satellite to ground detector, and presents the key achievements so far.
Secure communication networks are the critical infrastructure of the information age. To ensure secure communication between governmental institutions and other high-security environments, the German Federal Ministry of Education and Research (BMBF) initiated an ambitious project { the QuNET initiative. In a joint effort, the Max Planck Institute for the Science of Light (MPL), the German Aerospace Center (DLR) and the Fraunhofer Society aim to develop the technological basis of a German quantum key distribution (QKD) infrastructure. This paper describes the infrastructure used in a first link demonstrator within this project and how we achieved the transition from initial quantum transceiver concepts to first link experiments.
A worldwide growing interest in fast and secure data communications pushes technology development along two lines. While fast communications can be realized using laser communications in fiber and free-space, inherently secure communications can be achieved using quantum key distribution (QKD). By combining both technologies in a single device, many synergies can be exploited, therefore reducing size, weight and power of future systems. In recent experiments we demonstrated quantum communications over large distances as well as between an aircraft and a ground station which proved the feasibility of QKD between moving partners. Satellites thus may be used as trusted nodes in combination with QKD receiver stations on ground, thereby enabling fast and secure communications on a global scale. We discuss the previous experiment with emphasis on necessary developments to be done and corresponding ongoing research work of German Aerospace Center (DLR) and Ludwig Maximilians University Munich (LMU). DLR is performing research on satellite and ground terminals for the high-rate laser communication component, which are enabling technologies for the QKD link. We describe the concept and hardware of three generations of OSIRIS (Optical High Speed Infrared Link System) laser communication terminals for low Earth orbiting satellites. The first type applies laser beam pointing solely based on classical satellite control, the second uses an optical feedback to the satellite bus and the third, currently being in design phase, comprises of a special coarse pointing assembly to control beam direction independent of satellite orientation. Ongoing work also targets optical terminals for CubeSats. A further increase of beam pointing accuracy can be achieved with a fine pointing assembly. Two ground stations will be available for future testing, an advanced stationary ground station and a transportable ground station. In parallel the LMU QKD source size will be reduced by more than an order of magnitude thereby simplifying its integration into future free-space optical communication links with CubeSats.
In recent years, fiber-based quantum key distribution systems have emerged in a growing number of sectors. However, fiber optic links limit the distance that can be covered in point-to-point connections, so developments in free-space quantum communications are important. These can be used to establish free-space QKD links between buildings or to connect remote ground stations using satellite systems. In our research, we are developing an entanglement-based free-space QKD system based and we are simulating quantum communication satellite systems based on entanglement.
The development towards fault tolerant quantum computers has accelerated in recent years. It is therefore, reasonable to posit that quantum computers will be able to solve numerical problems previously unsolvable in a reasonable amount of time. This is particularly relevant in the context of factoring large composite numbers and solving the discrete logarithm problem. These two mathematical problems form the foundation for the vast majority of asymmetric encryption systems and key exchange procedures (such as RSA, DH, ECDH, ECDSA, and so forth). It is anticipated that quantum computers with cryptographic capabilities will become available within the next one or two decades. A significant number of high-security applications require the encryption of classified material beyond this timeframe. Consequently, the mitigation of the threats posed by quantum computers to classical encryption schemes has become a race against time, already. Currently two approaches are discussed to ensure quantum secure encryption and communications after the breakthrough of quantum computers. The first approach is called Post-Quantum-Cryptography (PQC). Here, new encryption and signature schemes are implemented based on mathematical problems which are hard to crack classically and by quantum computers. The second approach is based on a secure exchange of encryption keys and is referred to as Quantum Key Distribution (QKD). This approach utilizes the quantum mechanical properties of photons in a way that enables the sending and receiving parties to detect any attempts by an eavesdropper to record or alter the transmitted keys. If the successfully transferred keys are used only once for encryption unconditional security can be achieved in theory. Nevertheless, quantum key distribution (QKD) requires either dedicated fiber-optic lines that are solely used for the key exchange, commonly referred to as a dark fiber network or free-space links, which utilize a laser terminal and a telescope as the sender and receiver, respectively. Free-space links can be employed for mobile applications that facilitate quantum-secured communication with minimal deployment times over distances of several kilometers. Moreover, free-space links are utilized to exchange quantum keys between optical ground stations (OGS) and QKD satellites. By leveraging the in-orbit deployment of quantum keys, QKD enables the establishment of secure long- distance connections. DLR (Deutsches Luft- und Raumfahrtzentrum) is part of the Munich Quantum Network (MuQuaNet), which is a research dark fiber network situated in the metropolitan area of Munich. The project is spearheaded by the University of the Bundeswehr (Munich) and is operated in conjunction with a number of other research facilities and governmental institutions. The QKD network is comprised of multi-vendor QKD devices, including both prepare-and-measure and entanglement-based systems. DLR, in particular the German Space Operation Center (GSOC) assumed the task of demonstrating the use case of encrypting the ground segment for satellite operations employing QKD. This presentation will provide an overview of the current status of our work, including a technical explanation of the implementation and a general description of the approach used to encrypt part of our TMTC data streams as part of this QKD experiment.
Quantum key distribution (QKD) enables secure communication even in presence of quantum computers. Satellite based systems enable worldwide key distribution and connection of terrestrial quantum networks. In future, QKD satellite constellations can be operated to service ground users that are connected using an optical ground station. These QKD ground stations are assumed to be deployed in two scenarios. One is the option as end-user ground station, in which the ground user is directly connected to the satellite via the ground station. The other option is the use as a provider ground station, in which the ground user is connected via an intermediary fiber line. The performance of the satellite to ground QKD link depends on, amongst other, the environmental and infrastructural impacts of the site where it is located. Unlike in astronomical sites, the QKD Optical Ground Station (OGS) are not positioned in selected optimal environment, especially considering atmospheric turbulence and extinction. The QKD OGS mainly has to cope with the given environment instead. Knowledge of the site’s meteorological and infrastructural environment is important to assess performance of a QKD OGS when deployed. This paper discusses the most relevant aspects of a QKD OGS site characterization. These are atmospheric turbulence, atmospheric extinction, and background light. As a concrete example, the DLR Optical Ground Station Oberpfaffenhofen nearby Munich is used. Existing data is summarized, reviewed and needs for further data acquisition defined.