Metropolitan Quantum Networks: Linking Quantum Processors Across a City

Updated 2026-10-11 | 4 min read | QUANTUM (QNT) community

What "metropolitan" means

A metropolitan quantum network spans a city and its surroundings: roughly tens of kilometers. That scale is where fiber loss is still manageable without full quantum repeaters, and where the first useful applications could appear, such as linking research labs, hospitals, data centers and, later, quantum computers. It is the middle step between a lab bench and a national backbone. For the general idea, see the quantum internet.

Delft to The Hague: processors in different cities

In October 2024, QuTech, a collaboration between TU Delft and TNO led by Ronald Hanson, reported connecting two small quantum processors in Delft and The Hague. Each node used diamond spin qubits and ran independently, connected through a midpoint station over 25 km of deployed underground fiber. The team called it a record distance for quantum processors and the first time processors in different cities were linked. Partners included Fraunhofer ILT, which built a quantum frequency converter, plus OPNT, Element Six, Toptica and the Dutch telecom KPN. The team reported using a photon efficient protocol and extremely precise stabilization of the fiber, held to well under a micrometer over the 25 km. QuTech itself describes it as a rudimentary link: two nodes, not yet a network. Its press page does not give entanglement rates or fidelities.

Why a frequency converter?

Many qubits emit light at colors that fiber absorbs badly. A quantum frequency converter shifts a photon to the telecom wavelengths that travel best, without destroying its quantum state. This trick appears again and again in the work below, and it is what lets labs reuse the same cables that carry the internet.

Memories enter the picture

A 2026 arXiv paper, "A building block of quantum repeaters for scalable quantum networks" by Wen-Zhao Liu, Jian-Wei Pan and colleagues (listed as accepted for Nature), reports long lived trapped ion memories with a telecom interface. The authors report memory to memory entanglement established and maintained over a 10 km fiber, and metropolitan scale device independent QKD over 10 km that distilled 1,917 secret keys from about 405,000 Bell pairs. They also report a positive key rate over 101 km in the asymptotic limit, which they say extends the reachable distance by more than two orders of magnitude. Separately, a Tsinghua cold atom team reported in December 2024 heralded atom to photon entanglement across 12 km of fiber (a node to photon link, not yet memory to memory). We could not verify any other metropolitan memory result, so none is claimed here.

Testbeds underway

• The EU CAMERAS project aims to demonstrate light matter entanglement over a 50 km urban fiber, according to its project page.
• A German project running 2026 to 2027 targets entanglement of three quantum storage nodes, with a 52 km link as a key demonstrator.
• A New York area effort reports work on entanglement swapping across a five node, 270 km testbed between Long Island and New York City. I could only confirm a progress report, not a finished result.

Those are goals, not results, so watch for papers rather than headlines.

The honest limits

• Rates are low. Entanglement is made one heralded success at a time, and many attempts fail because photons are lost.
• Stability is hard. Fibers expand, vibrate and heat up, so timing and phase must be held with extraordinary precision.
• Few nodes. Two or three nodes is a link, not yet a network with routing and users.
• Lab hardware. Cryogenics, lasers and vacuum systems are not yet rack mounted telecom gear.

Why it matters for the future

A city network of small quantum processors is also a prototype for distributed quantum computing: the same entanglement links that secure a key can connect machines. Progress here depends on repeaters and memories and on better qubit platforms such as trapped ions. In a few years, the story may move from "first link" to "first small network". That is a thrilling direction, and the evidence so far is that it is real, even if early. Educational content only, not financial advice.

Sources and further reading

• QuTech: A rudimentary quantum network link between Dutch cities
• arXiv 2602.08472: A building block of quantum repeaters for scalable quantum networks
• CORDIS: EU project page (CAMERAS)
• Humboldt University: 52 km quantum repeater demonstrator project

Reported as of 2026-10-09. Quantum networking results are mostly lab or pilot demonstrations, and schedules slip. Check the primary papers and agency pages before relying on any figure. Nothing here is financial advice. QNT is an independent community memecoin and is not linked to Quantinuum Ltd or any lab, company or government.

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