Researchers are establishing the first quantum network based on tangles

A team of researchers from QuTech in the Netherlands reports the realization of the first multi-node quantum network, connecting three quantum processors. In addition, they demonstrated the proof of principle of key quantum network protocols. Their findings mark an important milestone for the future of the quantum internet and have now been published in Science.

The power of the Internet is that it allows any two computers on Earth to connect. Today, researchers in many laboratories around the world are working on the first versions of a quantum internet – a network that can connect any two quantum devices, such as quantum computers or sensors, over long distances. While today’s internet distributes information in bits that can be 0 or 1, a future quantum internet will use quantum bits that can be 0 and 1 at the same time.

“A quantum internet will open up a wide range of new applications, from awkward communication and cloud computing, with complete user privacy, to maintaining high-precision time,” says Matteo Pompili, Ph.D. student and a member of the research team. “And as with the Internet 40 years ago, there are probably many applications that we can’t predict right now.”

Towards ubiquitous connectivity

The first steps towards a quantum internet have been made in the last decade by connecting two quantum devices that have shared a direct physical connection. However, the ability to transmit quantum information via intermediate nodes (analogous to classic Internet routers) is essential for creating a scalable quantum network. In addition, many promising quantum Internet applications rely on tangled quantum bits distributed across multiple nodes. Confusion is a phenomenon observed on the quantum scale, fundamentally connecting particles at small and even large distances. It gives quantum computers their enormous computing power and is the fundamental resource for sharing quantum information on the future of quantum internet. By building their quantum network in the laboratory, a team of researchers from QuTech – a collaboration between Delft University of Technology and TNO – is the first to connect two quantum processors through an intermediate node and establish common links between several standards. alone quantum processors.

Operation of the quantum network

The rudimentary quantum network consists of three quantum nodes, at a certain distance within the same building. For these nodes to function as a real network, researchers had to invent a new architecture that would allow scaling beyond a single link. The middle node (called Bob) has a physical connection to both outer nodes (called Alice and Charlie), allowing for tangle connections with each of these nodes. Bob is equipped with an additional quantum bit that can be used as memory, allowing the storage of a previously generated quantum link while a new link is established. After establishing the Alice-Bob and Bob-Charlie quantum bonds, a set of quantum operations on Bob turns these bonds into an Alice-Charlie quantum bond. Alternatively, by performing a different set of quantum operations on Bob, the entanglement between all three nodes is established.

Ready for later use

An important feature of the network is that it announces the successful completion of these (intrinsically probabilistic) protocols with a “flag” signal. Such news is crucial for scalability, as in the future of the quantum internet, many of these protocols will have to be linked. “Once established, we were able to keep the resulting tangled states, protecting them from noise,” says Sophie Hermans, another team member. “It means that, in principle, we can use these states for the quantum distribution of the key, a quantum calculation or any other quantum protocol later.”

Quantum internet demonstrator

This first tangle-based quantum network provides researchers with a unique test bed for developing and testing hardware, software and quantum internet protocols. “The future of the quantum internet will consist of countless quantum devices and intermediate nodes,” says Ronald Hanson, who led the research team. “QuTech colleagues are already looking at future compatibility with existing data infrastructures.” In due course, the current approach to proof of principle will be tested outside the laboratory on existing telecommunications fiber – on QuTech’s Quantum internet demonstrator, of which the first metropolitan link is scheduled to be completed in 2022.

Top layer

In the lab, researchers will focus on adding more quantum bits to their three-node network and on adding higher levels of software and hardware layers. Pompili: “Once all the high-level control levels and interface layers for running the network have been developed, anyone will be able to write and run a network application without having to understand how lasers and cryostats work. That is the ultimate goal. ”