Quantum Repeater Global Backbone Network QuantumRelay Deep Dive: Intercontinental Quantum Key Distribution Achieves Commercial Use for the First Time

Quantum Repeater Global Backbone Network QuantumRelay Deep Dive: Intercontinental Quantum Key Distribution Achieves Commercial Use for the First Time

The security of quantum key distribution (QKD) is based on fundamental principles of quantum physics and is theoretically impossible to eavesdrop. However, quantum signal transmission distance in optical fiber is limited by photon loss, with a maximum single-fiber transmission distance of approximately 100 kilometers. Achieving intercontinental quantum communication requires quantum repeaters — devices that can "relay" quantum states without destroying their quantum properties.

The QuantumRelay backbone network, jointly deployed by QuantumCTek (affiliated with the University of Science and Technology of China) and the European Quantum Communication Infrastructure (EuroQCI), is solving this problem. The network has deployed 92 quantum relay nodes across China, Central Asia, and Europe, with a total link length exceeding 8,200 kilometers, achieving for the first time end-to-end commercial quantum key distribution between Beijing and Vienna.

"The core challenge of quantum repeaters is quantum storage — you need to preserve quantum states long enough to complete entanglement swapping between two relay nodes," said Professor Pan Jianwei of USTC. "Our relay nodes use rare-earth-ion-doped crystals as quantum memory, achieving a record coherence time of 1.2 seconds."

QuantumRelay's key generation rate is 800 bits per second, sufficient to support the high-security communication needs of financial institutions. The first commercial clients include the Bank of China and Erste Bank of Austria, using the service to protect encryption keys for cross-border financial transactions.

The network took three years to build, with a total investment of approximately 1.2 billion euros, jointly funded by China and the EU. The network uses a "satellite + optical fiber" hybrid architecture — quantum satellite relays for transoceanic segments and fiber-optic quantum repeaters for land segments.

However, QuantumRelay's operating costs remain high. Annual maintenance costs per kilometer of link are approximately 15,000 euros, making quantum-secure communication currently suitable only for financial and government scenarios with extreme security requirements. The team is developing low-cost silicon photonic chip-based repeaters, aiming to reduce costs by an order of magnitude within five years.