Quantum leap: China and South Africa establish intercontinental quantum satellite link

In a groundbreaking advance for quantum technology, scientists from China and South Africa successfully established the first-ever quantum satellite communication link between the two hemispheres spanning 12,900 kilometers (8,015.6 miles). This link, connecting Beijing and Stellenbosch University, now holds the title for the longest intercontinental quantum communication connection ever achieved (see video).

The feat was accomplished using China’s Jinan-1 quantum microsatellite and it marks several significant firsts: It’s the first quantum satellite connection in the Southern Hemisphere, and the inaugural secure quantum communication between the Northern and Southern Hemispheres. The secure exchange enabled the encrypted transmission of images, made possible through quantum key distribution (QKD), a technology grounded in the fundamental principles of quantum mechanics.

Developed in China, Jinan-1 is a small but technologically advanced satellite that weighs approximately 100 kilograms (kg) and carries a quantum payload approximately 23 kg, which is a substantial reduction compared to the 300-kg payload of the earlier Micius satellite. Orbiting at around 500 km above Earth, Jinan-1 can deliver highly accurate, low-error QKD—proving that cost-effective microsatellites can play a major role in the future of secure global communications. The optical ground stations have been miniaturized to around 100 kg, down from the 13,000 kg of previous setups, which can facilitate rapid deployment for diverse environments, including urban and mountainous regions.

Deployment and operation of the quantum satellite link

Unlike traditional cryptographic systems that rely on the difficulty of solving complex mathematical problems, quantum communication derives its security from the laws of quantum physics. QKD enables two parties to share encryption keys in a way that instantly detects any eavesdropping attempt. While optical fibers suffer from significant signal loss over long distances, satellite-based quantum links avoid much of this problem by operating within the upper atmosphere and outer space. This makes them an ideal platform for secure, long-distance communication.

Jinan-1’s single 850-nm laser diode operates at 625 MHz and uses external modulation to generate decoy-state BB84 quantum signals. The BB84 protocol, a foundational QKD scheme, relies on encoding qubits in two mutually unbiased polarization bases (e.g., rectilinear and diagonal). To enhance security, decoy states, photon pulses of varying intensity, were interleaved with signal states to protect against photon-number-splitting attacks. This design enhances integration, reduces side-channel vulnerabilities, and ensures robustness for space applications. To maintain signal fidelity, the system incorporates motorized wave plates to compensate for polarization changes due to satellite movement and fiber-induced transformations to achieve a quantum bit error rate (QBER) between 0.76 and 1.79%.

The satellite and ground stations use multiplexed bidirectional optical links (812-nm downlink and 1538-nm uplink lasers) for real-time synchronization and classical communication to enable immediate key distillation during satellite passes. This bidirectional link is crucial for real-time QKD because it enables the rapid exchange of auxiliary information necessary for key sifting, basis reconciliation, and error correction during the limited communication window of a satellite pass (typically <6 minutes). Unlike systems that perform post-processing hours after data collection, Jinan-1 enables immediate key distillation, making the secure key available right after the pass ends. Our QKD system uses low-density parity-check (LDPC) codes for error correction and privacy amplification, which minimizes data exchange and allows for the generation of secure keys within a single satellite pass.

A record-breaking achievement

The Jinan-1 mission builds upon the legacy of China’s earlier quantum satellite, Micius, which in 2016 demonstrated QKD over 7,600 km (4,722.4 miles) between China and Austria. The first successful quantum key exchange between Beijing and Stellenbosch occurred in October 2024. Clear skies and low humidity in Stellenbosch contributed to excellent signal quality and allowed the generation of over 1.07 million secure bits within a single satellite pass—an extraordinary milestone for quantum research on the African continent.

This volume of secure key bits within one pass not only demonstrates the robustness of the Jinan-1 system but also establishes a new performance benchmark for quantum satellite operations. Using the secure keys generated via Jinan-1’s quantum link, high-resolution images were encrypted and transmitted between ground stations. This demonstrated practical, real-time application of QKD for secure data transfer.

These milestones were achieved through a collaborative effort between the University of Science and Technology of China and Stellenbosch University. Key scientists include Professors Juan Yin and Jianwei Pan from China, along with Dr. Yaseera Ismail (me) and Professor Francesco Petruccione from South Africa. Our research underscores the importance of international partnerships in pushing the boundaries of scientific innovation.

Toward a quantum internet

The success of this intercontinental quantum link marks a major step toward achieving a global quantum internet that promises ultra-secure communication, distributed quantum computing, and advanced sensing capabilities. Our research showcases a scalable and practical approach to satellite-based QKD and paves the way for global quantum communication networks. The significant reductions in payload and ground station sizes make it feasible to deploy a constellation of such satellites, potentially enabling continuous, secure communication worldwide.

This achievement not only sets a new technological benchmark but also highlights the power of international collaboration in driving scientific discovery. The successful partnership between Chinese and South African researchers demonstrates how shared expertise, resources, and vision can lead to transformative advances in quantum technology.

FURTHER READING

Y. Li et al., Nature, 640, 47–54 (2025); https://doi.org/10.1038/s41586-025-08739-z.