Scientists at the Chinese Academy of Sciences and Delft University of Technology have achieved a landmark milestone in quantum networking — demonstrating quantum entanglement over a 1,000-kilometer fiber optic network connecting multiple cities. The achievement, published in Nature, represents the longest quantum network ever demonstrated and brings the vision of a global quantum internet significantly closer to reality.
What Is Quantum Entanglement
Quantum entanglement is a phenomenon where two particles become correlated in such a way that the quantum state of each particle cannot be described independently of the other, regardless of the distance separating them. When you measure the state of one entangled particle, you instantly know the state of its partner — a connection that Einstein famously called spooky action at a distance. This property can be used to create communication channels that are theoretically immune to eavesdropping, because any attempt to intercept the communication disturbs the quantum state and is immediately detectable.
The Technical Achievement
Maintaining quantum entanglement over long distances is extraordinarily difficult because quantum states are fragile and easily disrupted by environmental noise. The researchers overcame this challenge using quantum repeaters — devices that extend the range of quantum networks by creating entanglement between adjacent nodes and then connecting these local entanglements into a longer chain. The 1,000-kilometer network used 12 quantum repeater nodes spaced approximately 80 kilometers apart.
Applications of the Quantum Internet
The quantum internet will enable several revolutionary applications. Quantum key distribution allows two parties to share encryption keys that are guaranteed to be secure by the laws of physics — any eavesdropping attempt is immediately detectable. Distributed quantum computing allows quantum computers in different locations to work together on problems too large for any single machine. Quantum sensing networks can achieve measurement precision far beyond what is possible with classical instruments, enabling applications in navigation, medical imaging, and fundamental physics research.
Timeline to a Global Quantum Internet
Researchers estimate that a functional quantum internet connecting major cities within a single country could be operational within 5-10 years. A global quantum internet, requiring satellite-based quantum links to span oceans, is likely 15-20 years away. Several countries including China, the United States, the European Union, and Japan have launched national quantum internet programs with billions of dollars in funding, recognizing the strategic importance of this technology for national security and economic competitiveness.
