Researchers build multi-node quantum network

Researchers in the Netherlands have built a multi-node quantum network. The project is another step on the road to a quantum internet that uses quantum physics for communications.

The team, from research institute QuTech, strung together three quantum processors in a network that enabled each node to talk with the other using a physics process called quantum entanglement. This binds the properties of two quantum particles that are physically separate so the state of one instantly affects the state of the other.

The processors - which the researchers called Alice, Bob, and Charlie - used quantum bits (qubits) to set up their connection using a new quantum network protocol that the researchers created. Alice sends two qubits to Bob. The first establishes the entanglement, and the second is a memory qubit that Bob stores to set up its own connection to Charlie.

When that connection is made, Bob entangles its two qubits, forming a link that connects Alice, Bob, and Charlie together. The quantum networking protocol the researchers created also teleports the entanglement to both Alice and Bob, enabling them to talk directly to each other.

This rudimentary network is significant because, unlike conventional computers, quantum processors allow a single bit to simultaneously represent 0 and 1. This makes it possible to handle far greater computational loads than conventional computing and will pave the way for quantum cryptography that makes it practically impossible to crack an encrypted connection between two devices.

The researchers also created a 'flag' signal that will enable processors to indicate when they're connected. This is critical to scalability, they said.

The team conducted the initial demonstration within the same building, but the researchers look forward to demonstrating the protocol on traditional telecom fiber across their Quantum Internet Demonstrator. This is a network infrastructure it’ll use to demonstrate its quantum research over wider areas. The first metropolitan link is due to be turned on next year.

In the meantime, they will focus on developing higher-level software and hardware layers to build out the technology stack, they said.

QuTech is a collaboration between the Delft University of Technology and the Netherlands Organisation for Applied Scientific Research (TNO).

Last October, BT and Toshiba unveiled the first cross-site quantum data connection between two sites, using it to demonstrate how quantum key distribution could secure data traffic. In the US, The Department of Energy and the University of Chicago created a 52-mile link quantum link, with plans to develop it into a three-node network spanning 80 miles.