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Last week, a problem that has nagged quantum physicists for decades took a decisive step toward being solved: entanglement survived long enough to travel more than 100 kilometers through a repeater-enabled link.
Researchers at the University of Science and Technology of China, led by Jianwei Pan with key contributions from Qiang Zhang and Xiaohui Bao, reported experiments that combine long-lived quantum memory with entanglement-swapping techniques to create memory–memory links between distant nodes. The work, appearing in top journals, pushed device-independent quantum key distribution beyond the 100 km mark for the first time.
Why does that matter? Because photons attenuate in fiber. Loss eats entanglement. Without a way to pause and stitch quantum states together, secure quantum links stall after a few kilometers. Quantum repeaters are the patch: they store quantum information in local memories, then connect segments through entanglement swapping so the fragile correlations can span much longer distances.
What the USTC team achieved is not just a longer link but a practical step toward scalable repeater architectures. They produced high-fidelity atom–atom entanglement that lived long enough to complete the inter-segment operations required by real-world networks. That temporal buffer is crucial. It separates a laboratory curiosity from a component that can be reused in a multi-node chain.
The breakthrough enabled device-independent QKD, or DI-QKD, to operate over a record distance. DI-QKD is the gold standard for cryptographic security because it doesn't rely on trusting the internal workings of devices. Extending DI-QKD beyond 100 km demonstrates both robustness and an appetite for deployment in metropolitan and regional networks.
The experiment maps a clear route: long-lived quantum memories plus entanglement swapping equals repeaters capable of long-range, secure links.
Technically, the team combined optical interfaces with atomic memories and synchronized the exchange of entanglement across segments. The memory–memory entanglement was maintained on timescales longer than the communication and control delays, allowing reliable entanglement swapping. In plain terms: they bought time for quantum states so those states could be handed off rather than lost.
This achievement underscores two wider trends. One, China continues to invest heavily in quantum infrastructure and has produced a string of milestones in satellite links, metropolitan networks, and now repeater components. Two, the quantum internet is being assembled piece by piece: secure links, precision sensing, and distributed processing are converging into an architecture that could, in a decade or two, connect remote quantum processors and sensors with guaranteed security.
There are still engineering mountains to climb. Scaling from a two-node demonstration to multi-hop networks will demand better error correction, longer-lived and more efficient quantum memories, and integrated hardware that works outside a physics lab. But milestones like this change the conversation. They transform questions about feasibility into engineering roadmaps.
When the building blocks are reliable, the real game begins: who will design the protocols, standards, and commercial stacks that bring quantum-secure services to everyday users? The answer will shape not only cryptography but how we think about shared compute, sensing, and the flow of trust across the internet.
If repeaters keep improving at this pace, the next decade may be less about proving principles and more about connecting cities, laboratories, and industries with quantum-grade links.
Source: scitechdaily
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