Satellite-to-ground quantum communication using a 50-kg-class micro-satellite (1707.08154v1)

Abstract: Recent rapid growth in the number of satellite-constellation programs for remote sensing and communications, thanks to the availability of small-size and low-cost satellites, provides impetus for high capacity laser communication (lasercom) in space. Quantum communication can enhance the overall performance of lasercom, and also enables intrinsically hack-proof secure communication known as Quantum Key Distribution (QKD). Here, we report a quantum communication experiment between a micro-satellite (48 kg and 50 cm cube) in a low earth orbit and a ground station with single-photon counters. Non-orthogonal polarization states were transmitted from the satellite at a 10-MHz repetition rate. On the ground, by post-processing the received quantum states at an average of 0.14 photons/pulse, clock data recovery and polarization reference-frame synchronization were successfully done even under remarkable Doppler shifts. A quantum bit error rate below 5% was measured, demonstrating the feasibility of quantum communication in a real scenario from space.

• The paper introduces a pioneering experiment using a 50-kg micro-satellite to achieve quantum key distribution with a SOTA optical transponder.
• It employs non-orthogonal linear-polarization encoding and clock recovery techniques to overcome Doppler effects in LEO-based communications.
• The experiment achieved a QBER below 5%, validating the feasibility of cost-efficient, secure satellite-to-ground quantum communication.

Satellite-to-Ground Quantum Communication using a 50-kg-Class Micro-Satellite: A Summary

The paper focuses on an experimental investigation of satellite-to-ground quantum communication utilizing a low-cost, small-size 50-kg-class micro-satellite. This research addresses the growing demand for high-capacity communication networks, driven by an increasing number of satellite-constellation programs. The authors present the Satellite-to-Ground Optical Transponder Experiment using the micro-satellite SOCRATES, delivering promising outcomes for future quantum secure communications utilizing Quantum Key Distribution (QKD).

The experiment utilizes the SOTA (Small Optical TrAnsponder) terminal on the micro-satellite SOCRATES, which operates from a Low Earth Orbit (LEO) at roughly 650 km altitude. This transponder weighs merely 5.9 kg and transmits non-orthogonal polarization states at a 10-MHz repetition rate to a ground station equipped with single-photon counters. Among the significant achievements of this paper are the successful clock data recovery and polarization reference frame synchronization, even amid significant Doppler effects inherent in LEO-based communications. The QBER recorded was consistently below 5%, demonstrating the potential of micro-satellite platforms for effective quantum communication from space.

The paper elaborates on the evident advantages of laser communication enabled by compact satellite platforms. Quantum communication, due to its inherent security features, fits well into the lasercom model by providing a significantly enhanced secure data transmission channel compared to conventional microwave frequency bands. The initiative to miniaturize QKD technologies is advanced by this low-mass, cost-efficient demonstration, which seems poised to alter the paradigm of global-scale quantum-secured satellite communication.

Several critical technical challenges were surmounted during this experiment. The authors detail the use of non-orthogonal linear-polarization encoding emulating the B92 QKD protocol. Notably, the transmission system comprised linearly polarized laser diodes, Tx2 and Tx3, highly reliant on precise synchronization and tracking between the satellite and ground station. The beacon's non-orthogonal polarization format ensured that photons were prepared in quantum states suitable for secure communication, albeit the limitations posed by atmospheric interference and the Doppler effect.

The receiver configuration at the National Institute of Information and Communications Technology (NICT) Optical Ground Station (OGS) employs a complex assembly of beam splitters, polarizing beam splitters, and half-wave plates connected to four Single-Photon Counter Modules (SPCMs). This setup achieved photon detection with remarkable accuracy, allowing for post-processed alignment of the polarization angles and retransmission settings, ultimately substantiating low QBER rates.

The research presented in this paper lays groundwork for the theoretical and practical advancement of micro-satellite-based quantum communication. The promising outcomes highlight the technological feasibility of small-scale satellite platforms for reliable polarization and quantum state transmission, paving the way for integrating these technologies into larger satellite constellations. Future work will likely focus on optimizing the polarization tracking systems and further reducing error rates in more dynamic and less controlled environmental scenarios. This attempt serves as a pivotal step toward viable global-scale quantum communication secured by QKD, addressing current concerns over data security in satellite networks.