Quantum Internet Between Two Dutch Cities 25km Apart.

In a significant breakthrough, an international research team led by Ronald Hanson at QuTech has successfully demonstrated a quantum network link between two cities in the Netherlands. This achievement marks a crucial step towards building a future quantum internet, enabling the sharing of quantum information over long distances.

The team connected two small quantum computers between Delft and The Hague, creating a 25-kilometer quantum link using deployed optical internet fiber. This is the first time such quantum processors in different cities have been connected.

Key innovations included designing flexible systems that allow nodes to work independently over long distances, mitigating photon loss, and ensuring reliable confirmation of entanglement links. Companies involved in the project include Fraunhofer ILT, OPNT, Element6, Toptica, and Dutch telecom provider KPN. This milestone sets the stage for exploring quantum processor networks at metropolitan scale, paving the way for fundamentally new communication and computing capabilities.

Building the Quantum Internet: A Key Advance towards Metropolitan-Scale Networks

The quantum internet, a future network that enables the sharing of quantum information (qubits) over long distances, has taken a significant step forward by demonstrating a metropolitan-scale quantum link between two Dutch cities. An international research team led by QuTech has successfully connected two small quantum computers in Delft and The Hague, marking a key advance from early research networks in the lab towards a future quantum internet.

The current internet allows people to share information (bits) globally. In contrast, a future quantum internet will enable the sharing of qubits over a new type of network. Qubits can take not only the values 0 or 1 but also superpositions of those (0 and 1 simultaneously). Additionally, qubits can be entangled, which means they share a quantum connection, enabling instant correlations, no matter the distance. Researchers around the globe are working to build quantum networks that use these features to offer fundamentally new communication and computing capabilities in coexistence with the current internet.

The team, led by Ronald Hanson at QuTech, connected two small quantum computers between Delft and The Hague, a distance of 25 km. This achievement marks a record for quantum processors connected over such a long distance. To overcome the challenges of moving from lab experiments to realizing a quantum link between cities, the team had to design a flexible system that lets the nodes work independently over long distances, mitigate the impact of photon loss on the connection speed, and ensure reliable confirmation each time the entanglement link was successfully created.

To tackle the challenge of photon loss, the team established the quantum connection using a photon-efficient protocol that required very precise stabilization of the connecting fiber link. Co-author Arian Stolk explains that this challenge compares to keeping the distance between the earth and the moon constant with an accuracy of only a few millimeters. Through a combination of research insights and applied engineering, the team was able to solve this puzzle.

The project’s success was made possible by the team’s broad expertise, which included academia and industry partners. Co-author Kian van der Enden explains that Fraunhofer ILT developed a critical component for this demonstration, a new type of quantum frequency converter. Other partners, such as OPNT, Element6, Toptica, and Dutch telecom provider KPN, also contributed to the project’s success.

This result is an important milestone that addresses key scaling challenges for future quantum networks. The architecture and methods directly apply to other qubit platforms, including next-generation scalable qubits that the team is developing. The successful use of deployed, conventional internet infrastructure sets the stage for a new phase on the road towards a quantum internet.