The German state of North Rhine-Westphalia is setting up what is being called “the first node for the quantum internet of the future.” The system was delivered by the Fraunhofer Institute for Laser Technology (Fraunhofer ILT) who co-developed it with the Netherlands Organisation for Applied Scientific Research (TNO). The system will be tested and further developed, with the first regional connections expected to be made between Aachen, where it currently resides, and Jülich and Bonn. The international team, led by QuTech in Delft, the Netherlands, is developing metropolitan scale quantum networks to provide access to quantum computers for users from industry and research, to connect quantum computer platforms, and to make entangled qubits usable for the secure encryption of sensitive data. These networks have so far only been able to be implemented locally or regionally. Long-distance connections have proved elusive due to the lack of repeaters to amplify signals transmitted by individual photons without breaking quantum entanglement. The heart of the quantum internet node is a cultured diamond with specifically introduced nitrogen vacancies (NV centers). It emits single photons that can carry and transport information about the state of the qubit. Courtesy of Ralf Baumgarten/Fraunhofer ILT. The research team, led by QuTech and backed by TNO and the Technical University of Delft (TU Delft), demonstrated the connection between two quantum computers in Delft and The Hague with 25 km of underground optical fiber, and reproducibly created quantum entanglement along the fiber. Together, 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 at TNO in Delft, the new node was delivered to Aachen in mid-January. “We envision that metropolitan scale quantum networks will enable very powerful, secure connections between quantum computers and between quantum sensors,” said Bernd Jungbluth, who heads the Quantum Technologies strategic program at Fraunhofer ILT. The team anticipates the work will allow applications like distributed quantum computing, 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 currently only available to a limited extent. These, the researchers believe, could become a reality in the form of a connection from the Aachen node to the Helmholtz Quantum Center on the Jülich quantum campus. According to Jungbluth, a connection to the backbone of a central German test network in Bonn is also being considered. In addition to QuTech and Fraunhofer ILT, several companies were also involved in the project: OPNT B.V., the Dutch timing hardware specialist; Element6, a supplier of synthetic diamonds and qubit chip substrates; and TOPTICA Photonics AG, a specialist for highly stable lasers.