QKD via QUBE satellite
The small QKD satellite QUBE was recently able to establish a connection of the quantum modules to the ground station in order to demonstrate the use of tamper-proof QKD keys now also satellite-based from space over long distances for worldwide transmission for research purposes. QUBE is a joint project of the Center for Telematics (ZfT) with FAU, the Max Planck Institute for the Science of Light and LMU with the participation of DLR and OHG GmbH, which is funded by the German Federal Ministry of Research, Technology and Space (BMFTR).
The 3U-CubeSat is very compact, by reducing both the satellite and the necessary laser technology in size and weight to a total of 3.5 kg. In comparison, fiber-based QKD devices weigh over 10 kg. In addition, the quantum hardware, which is normally very sensitive and prone to environmental changes, now has to withstand temperature fluctuations, vibrations and space radiation. The range of 480 km to the ground station is also higher than that of fiber-based devices with higher losses, where a maximum of 150 km is possible without intermediate amplification.
The biggest challenge, however, lies in the actual key exchange with the ground station. The laser in the satellite must be able to focus at orbital altitude on the receiver with a diameter of only 80 cm for 10 minutes at an orbital speed of 27500 km/h. This is achieved with the highest accuracy with the help of a position control system in the satellite.
QUBE is just the beginning: QUBE II is scheduled to be launched in the summer of 2026. QUBE I was only intended to demonstrate the targeted connection with a ground station. The aperture is too small for proper QKD communication. The 6U-CubeSat QUBE II is now much larger and contains improved optical and quantum components also for the necessary QKD post-processing.
In the future, there are likely to be several tests with satellites for quantum-safe communication in space to complement the ground infrastructure: Colt, Nokia and Honeywell are planning tests for commercial solutions (https://www.security-insider.de/quantenschutz-aus-dem-all-a-db4eab7e99c5b98cb65e1306815adec6/), while Fraunhofer IOF has designed a 16U satellite CubEniK (https://www.iof.fraunhofer.de/de/presse-medien/pressemitteilungen/2024/CubEnik.html).
further informations:
https://xqp.physik.uni-muenchen.de/research/quant_crypto/2024_qube_mission/index.html