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Germany setting up first node for future quantum internet

23 Jan 2025

Marking International Year of Quantum, Fraunhofer ILT to verify node and make first connections in country.

Just in time for the start of UNESCO’s International Year of Quantum Science and Technology 2025 (“IYQ”), German region North Rhine-Westphalia is setting up what it calls “the first node for the quantum internet of the future”.

A team from the Fraunhofer Institute for Laser Technology (ILT) brought the system, developed in Delft in the Netherlands, to its headquarters in Aachen, Germany, to test and develop it further and establish the first regional connections to the region of Jülich and Bonn.

Quantum computers will not replace conventional PCs in the foreseeable future as today’s quantum platforms are simply too expensive to operate, says the ILT. However, an international team led by QuTech in Delft, the Netherlands, is driving forward the development of so-called “metropolitan scale quantum networks” – to provide many users from industry and science with access to the powerful computers, to connect different quantum computer platforms with each other.

Cutting-edge research

The research team led by Ronald Hanson from QuTech, backed by TU Delft and research group TNO, has recently reported a breakthrough. It has not only connected two quantum computers in Delft and The Hague with 25 km of underground optical fiber but also was able to reproducibly create the state of quantum entanglement along the fiber. In Delft, this entanglement is generated with single photons emitted by qubits in the network nodes. The qubits – known as diamond spin qubits – are the spin of individual electrons captured in the crystal lattice of artificial diamonds.

The spin is trapped in specifically introduced nitrogen vacancies (NV centers), where it is controlled with microwave signals and magnetic fields and can be read out using lasers. The readout results in the emission of a photon with a wavelength of 637 nm, which carries and can transport information about the state of the qubit.

One of the key challenges is to guide the photons emitted in all directions into the optical fiber – efficiently, with low noise and beyond the usual telecom wavelengths. To accomplish this, ILT developed not only a virtually noise-free quantum frequency converter but also a specifically shaped optical system integrated directly into the diamond chip.

But there were many other challenges. For example, establishing a stable connection, which must maintain accuracies in the order of one wavelength of the photons over the 25 km glass fiber; according to QuTech, this is comparable to keeping the distance between the earth and the moon constant to within a few millimeters.

First node in Aachen

In addition to the connection between The Hague and Delft, the cooperation has now implemented a further quantum internet node optimized using the experience gained with funds from the North Rhine-Westphalian funding project N-QUIK.

Among other things, TNO and Fraunhofer ILT have revised the design so that individual components are now easier to replace during testing. The Aachen-based institute also contributed various optical assemblies. After assembly and a test operation phase including its characterization in Delft, the new node found its way to Aachen in mid-January.

“This project gives us a practical test field where we want to develop this technology to market maturity together with partners from industry and science,” said Dr. Bernd Jungbluth, who heads the Quantum Technologies strategic program at ILT. “We envision that metropolitan scale quantum networks will enable very powerful, secure connections between quantum computers and between quantum sensors.”

Applications such as distributed quantum computing are conceivable, which interconnects several computers to form a quantum system to quickly scale their capacity and performance. Quantum networks are also important with regard to secure remote access to quantum computers, which are initially only available to a limited extent.

Sacher Lasertechnik GmbHMad City Labs, Inc.Omicron-Laserage Laserprodukte GmbHAlluxaHÜBNER PhotonicsLaCroix Precision OpticsCHROMA TECHNOLOGY CORP.
© 2025 SPIE Europe
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