The promise of a quantum internet — a revolutionary communications network that would be unhackable by design — has moved closer to reality with a major scientific breakthrough. Researchers have successfully linked two quantum networks together, creating a system capable of securely connecting 18 people using the counterintuitive principles of quantum physics. While the achievement represents a significant technical milestone, experts caution that scaling this technology to create a global quantum internet faces enormous practical challenges.
What is a quantum internet?
Unlike today’s internet, which transmits classical information, a quantum internet would transmit quantum information using particles called photons. The foundation of this technology is quantum entanglement, a phenomenon where particles become linked so that the state of one instantly influences the state of another, no matter how far apart they are. This property could enable:
- Unhackable communications : Information encoded in quantum states cannot be copied without detection
- Distributed quantum computing : Quantum computers could work together across distances
- Ultra-precise sensing networks : Quantum sensors could be linked for unprecedented accuracy
But creating a functional quantum network is far more complex than building a conventional network. Quantum entanglement is fragile, and maintaining it across large distances requires sophisticated technology. Quantum information cannot be amplified like classical signals — measuring a quantum particle typically destroys its delicate state.
The breakthrough: linking quantum networks
Researchers led by Xianfeng Chen at Shanghai Jiao Tong University have demonstrated a method to connect two independent quantum networks into a single, unified system. Their approach involved:
- Building two separate quantum networks, each containing 10 nodes (quantum devices)
- Ensuring all nodes within each network were entangled with one another
- Sacrificing one node from each network to establish entanglement between the two systems
- Creating a single network with 18 active nodes, all pairwise entangled
This achievement demonstrates a crucial capability: networking multiple quantum systems together. As lead researcher Chen explained, “Our approach offers a crucial capability for quantum communication across different networks and is advantageous for building a large-scale quantum internet that enables communication among all users.”
How does it work?
The process used to link the networks is called entanglement swapping. Here’s what makes it challenging:
- Quantum entanglement requires delicate photon states
- The Bell measurement needed for entanglement swapping destroys the measured photons
- Maintaining precise timing between measurements requires cutting-edge technology
As Siddarth Joshi, a quantum communication expert at the University of Bristol, notes: “This is not the first time entanglement swapping has been shown… What they have done is they have created a scheme where you can do the swapping between the networks in a bit more of a convenient way.”
The path forward: scaling challenges
While the technical achievement is impressive, scaling this to a global network faces significant hurdles. Robert Young, a quantum technology expert at Lancaster University, offers a cautious perspective: “It’s just so far from practical, and it’s so far from anything that could be implemented in the real world… The claim of the paper is that this is the future of how you might fuse quantum networks, but there are just so many challenges to solve in achieving that that it’s frustrating.”
The most immediate technical challenge is the need for quantum repeaters. Unlike conventional signals that can be amplified, quantum signals weaken over distance and cannot be boosted without destroying the quantum information. Young explains: “Practically, building a quantum network, we know we’re really going to need some form of quantum repeater — something this network demonstration doesn’t address.”
Quantum internet: still years away?
Despite the impressive technical achievement, the researchers acknowledge the challenges ahead. In their paper, they describe their work as “a crucial capability” but recognize that scaling to global networks will require additional breakthroughs.
The development represents a significant step in the right direction, but as quantum technology expert Siddarth Joshi notes, it addresses only one aspect of the quantum internet puzzle: “Both [connecting devices over distance and networking many devices] are very important.”
While we’re still years (likely decades) from a fully functional quantum internet, this breakthrough demonstrates the feasibility of linking multiple quantum systems — a crucial capability for the future development of quantum communication networks.
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