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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Quantum Communication with Photonic Integrated Circuits on a CubeSat

Jonas Pudelko, Ömer Bayraktar, Joost Vermeer, Luca Vill, Imran Khan, W. Boxleitner, Stefan Petscharnig, Christoph Pacher, Gerd Leuchs, Christoph Marquard

Published Jun 23, 2025• 0 citations
Publisher

Abstract

Exponential losses limit the range of fiber based quantum key distribution (QKD) systems to several hundreds of kilometers [1]. In contrast, a satellite based QKD infrastructure could cover intercontinental distances and would enable world wide secure communication [2]. However, the profitability of a commercial system is highly dependent on its size, weight and power requirements. Photonic integration [3] is a well suited option as it allows the integration of all required optical components for a QKD system onto a single photonic integrated circuit (PIC). In this work, we present our CubeSat payload consisting of a PIC based sender for modulated weak coherent states as well as a quantum random number generator (QRNG). It was launched in 2024 as part of the QUBE mission [4], which aims for the demonstration of novel miniaturized building blocks for satellite quantum communication.

DOI
10.1109/cleo/europe-eqec65582.2025.11110274

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Exponential losses limit the range of fiber based quantum key distribution (QKD) systems to several hundreds of kilometers [1]. In contrast, a satellite based QKD infrastructure could cover intercontinental distances and would enable world wide secure communication [2]. However, the profitability of a commercial system is highly dependent on its size, weight and power requirements. Photonic integration [3] is a well suited option as it allows the integration of all required optical components for a QKD system onto a single photonic integrated circuit (PIC). In this work, we present our CubeSat payload consisting of a PIC based sender for modulated weak coherent states as well as a quantum random number generator (QRNG). It was launched in 2024 as part of the QUBE mission [4], which aims for the demonstration of novel miniaturized building blocks for satellite quantum communication.
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In 2017, the Micius mission [1] showed that satellite quantum key distribution (QKD) can surpass the range limit of fiber-based QKD [2]. Due to the high launch cost of satellites the cost of these systems would be reduced significantly if the size, weight and power of the satellites could be reduced. This requires the use of new integration technologies, like the miniaturized modules based on photonic integrated circuits (PIC) tested in the QUBE mission [3], [4]. Using the knowledge gained there, the QUBE-II mission aims to launch an 8U CubeSat(10×20×40cm3)(10\times 20\times 40\text{cm}^{3})(10×20×40cm3)with the goal of performing QKD between the cubesat and an optical ground station [5].
Quantum key distribution (QKD) and quantum random number generation (QRNG) will play a key role in the future of data communication security. QKD can be used by trusted parties to share a secret key, leading to long-term secure communications. QRNG allows the production of fully unpredictable and certifiable random numbers, which can be used in numerous applications, including cryptography and large stochastic simulations. Both QKD and QRNG can be implemented using commercially available photonic components, which are mostly bulky and assembled into a discrete module. Although this approach can benefit from the superior performance and maturity of each individual component, it does not guarantee the large-scale deployment and commercial viability of the technology. A preferable alternative relies on integrating some or all functionalities in a single photonic integrated circuit (PIC) fabricated at the wafer scale, in this way reducing size, weight, complexity, cost, and power consumption. Integrated photonics can thus dramatically improve the performance and reliability of QKD systems and QRNG devices. Here, we review recent literature on designs, related materials, and fabrication processes, which is representative of state-of-the-art PIC-based QKD and QRNG. We conclude the paper by pointing out the challenges that need to be addressed in the future for reaching a wide-scale deployment of these integrated technologies.
In a world of global satellite communication networks, it is crucial to ensure the security of these data links. QUBE is a project that will develop and launch a CubeSat for the downlink of strongly attenuated light pulses, with encoded quantum information, which can be used for the exchange of encryption keys. This 3U Pico-Satellite will be built using the UNISEC-Europe standard, which has been proven to provide a robust framework for increased reliability for CubeSat missions. In addition to advanced reaction wheels for precision pointing, the satellite will be carrying the DLR-OSIRIS optical downlink system as well as dedicated payloads for testing components required for quantum key distribution. A miniaturized quantum random number generator (QRNG) will create a sequence of numbers, which can be used to set the quantum states of the light. The light pulses will then be downlinked to the optical ground station at DLR in Oberpfaffenhofen, Germany, which is equipped with the corresponding components for receiving the quantum states. Additionally, the random numbers will partially be made available via an RF downlink. This will allow evaluating the link loss as well as the noise and errors in the transmission of quantum signals. In QKD, due to the underlying quantum mechanics, any attempt of reading the quantum states will alter them, which makes interceptions easily detectable. The quantum communication experiments will evaluate whether secure communication links are possible even on a CubeSat scale. A major challenge for building the required CubeSat is the attitude determination and control system that will provide precise pointing. This work will outline detailed mission requirements as well as the chosen subsystems for tackling these challenges in order to deliver a successful mission.
Satellite-based Quantum Key Distribution (QKD) can be used to deliver information-theoretically secure keys for cryptographic applications, no matter where end-users are located. Several space missions using this concept have shown feasibility of systems and component technologies. The QUBE-II mission, with a planned launch in Spring 2026, uses an economic CubeSat platform to show the possibility of a global secure communication by simple means. This paper presents the optical system design of the QUBE-II laser communication terminal (LCT). It is based on the previous developments for the CubeL mission (launched in 2021), for CubeISL, and for the precursor mission QUBE-I (launched in 2024). The 2.5U LCT is integrated into an 8U CubeSat and serves as transmit system for two Alice modules operating at 850 nm and in optical L-band1, 2 respectively. At the same time, bi-directional classical links are used for link acquisition, tracking, and data transmission. With its 85 mm aperture and an 800 mm receiver telescope on the ground station, the antenna gain is sufficiently high enough to perform QKD links. The LCT’s optical system is designed based on a commercially available reflective telescope in combination with custom-designed lenses. It integrates several fiber-optical and electrical components for wavelength combination, wavelength splitting, tracking, and uplink data reception into a compact design. The Alice payloads are connected to the LCT by optical fibres allowing a flexible placement of the modules within the satellite bus. Collimators couple the light into free-space beams which are co-aligned and interfaced to the transmit telescope. In addition to the optical system design, this paper provides further information about the integration of the optical into the mechanical system, and the performed functional and qualification tests.