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Zhang Tong

Chinese researchers say they have found a viable pathway to building long-distance quantum communication networks.
In a study published this week in Nature, a team from Peking University said it had developed a prototype networking capacity that could communicate over distances of more than 3,700km (2,300 miles).
Quantum key distribution (QKD) is regarded as the gold standard for secure communication – any attempt at eavesdropping inevitably leaves detectable traces, regardless of distance or the number of intermediate devices involved.
But despite its theoretical promise, QKD has struggled to overcome barriers such as limited range, prohibitive equipment costs or the inability to serve multiple users efficiently.
Existing systems rely on a series of “trusted relay nodes” – essentially stations that handle quantum keys along the route.
While functional, these nodes introduce potential security vulnerabilities, much like packages that change hands at multiple distribution centres.
The team said its new approach had eliminated the need for such relays.
At the server side of the system lies a “super optical comb”, a low-frequency chip smaller than a fingernail that generates dozens of ultra-stable laser lines operating at the same frequency.
If traditional quantum communication can be likened to two people shouting across a valley amid wind and rain, this optical comb serves as a perfectly synchronised metronome, enabling every user device to operate from an identical, unwavering time base with a line width as low as 40 hertz.
On the client side, the team built 20 independent quantum transmitter chips, which integrated a complete suite of functions allowing them to serve as quantum telegraph operators.
Operating in pairs, they can receive timing signals from the central optical comb, encode key information onto light pulses and send them through 370km of optical fibre to a central server.
What set this new system apart was the relative ease and cheapness of making it.
Historically, QKD systems have been custom-built, making them prohibitively expensive and impractical for widespread use.


By contrast, the researchers said both server and client-side chips showed high performance, reproducibility and operational yield – critical prerequisites for scalable quantum devices – and could be fabricated from mature industry wafers.
The experimental results underscored the system’s robustness. Of the 120 modulators on 20 randomly selected client chips, 117 functioned correctly, yielding a 97.5 per cent operational success rate.
Each user pair could communicate across 370km, and the aggregate networking capability across all 20 users reached 3,700km.
Researchers hope this model can become the backbone for intercity quantum communications supporting hundreds of users without the need for trusted relays.
An additional advantage lies in its compatibility with existing fibre infrastructure, which would allow quantum signals to share the same network as traditional internet traffic, removing the need for specialised cabling.
However, the system is not yet ready for everyday office or household use because it is only able to operate under carefully maintained laboratory conditions.
Nevertheless, the research team has already charted the next phase: integrating single-photon detectors and optical frequency shifters onto the server chip and expanding the number of microcomb channels.
Theoretically, this platform could be scaled up to support hundreds of users, with individual quantum links of up to 1,000km.


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China

Team from Peking University says its model could allow for ultra-secure communications across thousands of kilometres


Team from Peking University says its model could allow for ultra-secure communications across thousands of kilometres.


Quantum computing

Peking University

Chinese scientists find path for long-distance quantum communications network

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Team from Peking University says its model could allow for ultra-secure communications across thousands of kilometres

Team from Peking University says its model could allow for ultra-secure communications across thousands of kilometres