First quantum network built in the world

Scientists from Delft have created the world’s very first quantum network. Never before have three quantum processors been connected in a network. This achievement is a step forward towards a larger quantum internet.

When computers calculate with 0 or 1 bits, quantum computers use quantum bits (or qubits). They can also be a combination of 1s and 0s. In theory, these “quantum states” give quantum computers enormous computing power.

You need a quantum internet to connect different quantum computers and enable information exchange. This allows you to further increase the combined computing power of the computers.

Crypt

What also makes the quantum internet interesting is the ability to transmit information securely. Another quantum property is important for this: the entanglement of particles. You can connect quantum particles to each other. If you then measure these connected particles, you will find consistent values ​​for the two particles; if one is 0, the other is 1 and vice versa.

Quantum states (in which this information of zeros and ones is packed) cannot be simply copied. If you do, it will cause disruption. When reading the two entangled qubits, these values ​​no longer match. If the zeros and ones match, you know you weren’t bugged. In this way, entangled qubits are ideally suited for the encrypted transmission of sensitive information.

Moreover, the entanglement of qubits still has very low chances of success for the inhabitants of Delft: it succeeds about ten times per second. The advantage is that in their configuration they actually receive a signal when entanglement is successful. This is an important property if the quantum network becomes operational on a larger scale in the future.

Increase

In the world’s first quantum network, Thursday published in Science, the three quantum processors are linked. Scientists named the three points Alice, Bob, and Charlie for convenience. Bob forms a physical connection with Alice and Charlie.

Importantly, Alice and Charlie can also be related, the scientists concluded, even though there is no physical connection between them. They need Bob for this. Bob is equipped with a special memory qubit. This one remembers the entanglement between Alice and Bob, while Bob becomes tangled up with Charlie.

This property is also needed from a future perspective, if such a quantum lattice is to be scaled up. You want to be able to establish a connection between two processors that are not physically connected. Compare it with today’s internet: there isn’t a huge cable that connects everyone in the world directly to a computer.

What the Delft researchers have now done and measured is not yet a large-scale quantum internet. In addition, the three different processors only consist of one or, in Bob’s case, two qubits, and are therefore not comparable to a future quantum computer of size, where we speak of millions or billions. of qubits. But this is the next step towards a bigger quantum lattice.

An advance

“ It is truly a technical tour de force and a step forward towards the quantum lattice that Delft QuTech hopes to achieve in the Randstad, ” says the physicist Carlo Beenakker from the University of Leiden. “It is necessary to have this network in five years, and it will work.”

Beenakker does not wish to comment on a term for further dissemination of the quantum internet. “It’s a developing technology, you can’t put a date on it.” In addition to science and technology, there are also many other factors that influence the practical application of the quantum network. “The question is not only whether you can do it, but also whether you want to.”

For banks, governments and the military, the more secure means of communication offered by the quantum internet actually has added value, says Beenakker. It is a very practical application, for which organizations such as banks would already be willing to pay money for it. Time will tell if every home will soon be connected to the quantum internet.

“We can be proud of this, it is really a milestone,” says Beenakker. “China is spending billions on it, even has a satellite in space for the quantum internet. Yet we in the Netherlands have a head start in this area. “