April 23, 2024

QuTech, a team of Dutch researchers, has reported the realization of the first multi-node network connecting three quantum processors. They also demonstrated key protocols for quantum network protocols in a proof of principle demonstration. These findings are a significant step towards the future quantum Internet and were published inĀ Science.

The quantum Internet

The Internet’s power is its ability to connect any two computers on Earth, which allows for applications that were unimaginable decades ago. Researchers in many laboratories around the globe are currently working to create the first version of a quantum Internet. This network can link any two quantum devices over long distances. While the Internet presently distributes information in bits, which can be 0 or 1, a future quantum Internet will use quantum bits that can be 0 and 1. Matteo Pompili is a Ph.D. student and part of the research team. “A quantum internet will allow for a wide range of new applications, including unhackable communication, cloud computing with complete privacy, high-precision time-keeping, and cloud computing with complete security.” “And, like the Internet 40 years back, there are likely many applications we do not know about right now,” he said.

Towards ubiquitous connectivity

In the last decade, two quantum devices connected by a physical link were used to make the first steps toward a quantum Internet. Transmitting quantum information via intermediate nodes (analogous routers in the classic Internet) is crucial to create a scalable quantum network. Many promising applications for quantum Internet rely on entangled bits. These quantum bits can be distributed among multiple nodes. Entanglement, a quantum phenomenon that fundamentally connects particles at small and great distances, is observed at the quantum level. Entanglement is a critical resource for sharing quantum information over the future Internet. It gives quantum computers enormous computational power. A team of QuTech researchers, collaborating with Delft University of Technology (TNO) and QuTech, has created a quantum network in their lab. They are the first to connect two quantum processors via an intermediate node. Also, they have established shared entanglement among multiple stand-alone processors.

Operation of the quantum network

The rudimentary network of quantum nodes consists of three at different distances within the same building. Researchers had to create a new architecture that allows scaling beyond one link to make these nodes work as a real network. The middle node, Bob, is physically connected to Alice and Charlie. This allows for entanglement links to each node. Bob has an additional quantum bit that can serve as memory. This allows a previously created quantum link to be saved while a new one is made. Once the quantum links Alice Bob and Bob-Charlie have been established, a series of quantum operations by Bob transforms them into a quantum Link Alice-Charlie. Bob can perform a different set of quantum operations to establish entanglement between all three nodes.

Ready for use

The network’s “flag signal” announces the completion of these (intrinsically probabilistic) protocols. This is vital for scaling since many protocols of a quantum internet must be concatenated. Sophie Hermans, another member, says that once the protocol was established, preserving the entangled states and protecting them from noise as possible. This means that we can use these states for quantum key distribution and computation and any subsequent quantum protocol.

Quantum Internet Demonstrator

Using this first entanglement-based network, researchers have a unique testbed to develop and test quantum internet protocols, software, and hardware. Ronald Hanson, the researcher who led the team, said that “the future quantum internet” will include many quantum devices and intermediate nodes. “Colleagues from QuTech are already investigating future compatibility with existing infrastructures,” says Ronald Hanson, who led the research team. The current proof-of-principle approach will be tested on existing telecom fiber on QuTech’s Quantum Internet Demonstrator. The first metropolitan link is expected to be completed by 2022.

Higher-level layers

Researchers will use the lab to add more quantum bits and higher-level software and hardware layers to their three-node network. Pompili says that once all the interface and control layers necessary to run the network are developed, anyone can write and manage a network application. This is the ultimate goal.

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