Entanglement-based secure quantum cryptography over 1,120 kilometres

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Satellite Communication

Background:

• Quantum Key Distribution (QKD) offers theoretically secure key sharing but is limited by distance in terrestrial networks.
• Existing methods like trusted relays extend QKD range but introduce security vulnerabilities.
• Satellite-based QKD and entanglement distribution are promising for secure long-distance communication but face efficiency challenges.

Purpose of the Study:

• To demonstrate entanglement-based Quantum Key Distribution (QKD) between two ground stations over a record distance without trusted relays.
• To enhance the efficiency and security of satellite-based entanglement distribution for practical QKD applications.
• To achieve a finite secret-key rate for secure communication over 1,000 km.

Main Methods:

• Utilized the Micius satellite for bidirectional downlinks to distribute entangled photon pairs to two ground observatories.
• Developed high-efficiency telescope and follow-up optics to improve link efficiency for entanglement distribution.
• Implemented ground receivers designed for fair sampling and immunity to side-channel attacks to ensure key security.

Main Results:

• Successfully demonstrated entanglement-based QKD between two ground stations separated by 1,120 kilometers.
• Achieved a finite secret-key rate of 0.12 bits per second.
• Increased the secure terrestrial QKD distance by tenfold compared to previous methods.

Conclusions:

• Satellite-based entanglement distribution can enable secure, long-distance QKD without relying on trusted relays.
• The developed technology significantly improves link efficiency and practical security of QKD systems.
• This approach represents a major advancement for global secure quantum communication networks.