Physicists say this futuristic, super-secure network could be useful long before it reaches technological maturity
A future ‘quantum internet’ could find use long before it reaches technological maturity, a team of physicists predicts.
Such a network, which exploits the unique effects of quantum physics, would be fundamentally different to the classical Internet we use today, and research groups worldwide are already working on its early stages of development. The first stages promise virtually unbreakable privacy and security in communications; a more mature network could include a range of applications for science and beyond that aren’t possible with classical systems, including quantum sensors that can detect gravitational waves.
The quantum difference
The researchers argue that the technology, which would complement rather than replace the existing Internet, could eventually become widespread both for large users, such as university laboratories, and for individual consumers, although they do not give a time scale.
This stands in contrast with quantum computers, they say—another futuristic technology that physicists are feverishly working on, aiming to build machines that can outperform classical computers. “In the quantum-computing domain, it’s much more all or nothing,” says theoretical physicist Stephanie Wehner, who co-authored the paper with her Delft colleagues David Elkouss and Ronald Hanson.
Stefanie Barz, a quantum physicist at the University of Stuttgart in Germany, agrees. It’s difficult to predict which technology will come first, she and others say—a widely adopted quantum internet or useful quantum computers. But quantum networks have a big advantage, Barz says, in that “such a network can be built step by step, and different functionality can be added in each step”.
The roadmap also aims to establish a common language for a field that involves researchers with disparate backgrounds, including information technology, computer science, engineering and physics. “People talk about quantum networks to mean vastly different things,” says Hanson, an experimental physicist who is co-leading the Delft group’s push to build a quantum-internet demonstration that will link four Dutch cities.
Rodney Van Meter, a quantum network engineer at Keio University in Tokyo, says that the paper helps to clarify the field’s goals. “It gives us a new vocabulary for understanding what we are developing.” And the way the document spells out the applications can also help researchers explain their proposals to potential investors, he says. “With this roadmap, we can have this conversation.”
Quantum networks and quantum computing share many concepts and techniques. Both take advantage of phenomena that have no analogue in classical physics: for example, a quantum particle such as an electron or a photon can be in one of two well-defined states of spinning, clockwise or anticlockwise—but also in a simultaneous combination of both, called a superposition. And two particles can be ‘entangled’, in which they share a common quantum state. This makes them act in seemingly coordinated ways (such as spinning in opposite directions) even when they are separated by vast distances.
The Delft team has laid out six stages for the evolution of the quantum internet.
The first—which they say is a sort of stage 0 because it does not describe a true quantum internet—is a network that enables users to establish a common encryption key, so that they can share their (classical) data securely. The quantum physics occurs only behind the scenes: the service provider uses it to create the key. But the provider also knows the key, which means that users have to trust it. This type of network already exists, most notably in China, where it extends over some 2,000 kilometres and connects major cities including Beijing and Shanghai.
In stage 1, users will start getting into the quantum game, in which a sender creates quantum states, typically for photons. These would be sent to a receiver, either along an optical fibre or through a laser pulse beamed across open space. At this stage, any two users will be able to create a private encryption key that only they know.
The technology will also enable users to submit a quantum password, for example, to a machine such as an ATM. The machine will be able to verify the password without knowing what it is or being able to steal it.
Stage 1 has not been tried on a large scale, but it is already technologically feasible at the scale of small cities, Wehner says, although it would be very slow. A group led by Pan Jian-Wei at the University of Science and Technology of China in Hefei made the world record for this kind of transmission in 2017, when they used a satellite to link two laboratories more than 1,200 kilometres apart.
In stage 2, the quantum internet will harness the powerful phenomenon of entanglement. Its first goal will be to make quantum encryption essentially unbreakable. Most of the techniques that this stage requires already exist, at least as rudimentary lab demonstrations....MUCH MORE