From Santa Barbara, California, to Hefei, China, scientists are developing a new kind of computer that makes today’s machines look like toys.
Harnessing the mysterious powers of quantum mechanics, the technology will complete tasks in minutes that even supercomputers couldn’t complete in thousands of years. In late 2019, Google unveiled an experimental quantum computer that showed it was possible. Two years later, a lab in China did much the same.
But quantum computing will not reach its potential without the help of another technological breakthrough. Call it a “quantum internet” – a computer network that can transmit quantum information between distant machines.
At Delft University of Technology in the Netherlands, a team of physicists has taken an important step towards this computer network of the future, using a technique called quantum teleportation to transmit data across three physical locations. Previously, this was possible with just two.
The new experiment indicates that scientists can extend a quantum network across an ever-increasing number of locations. “We are now building small quantum networks in the lab,” says Ronald Hanson, the Delft physicist who directs the team. “But the idea is to eventually build a quantum internet.”
Their research, unveiled this week with a paper published in the scientific journal Nature, demonstrates the power of a phenomenon Albert Einstein once thought impossible. Quantum teleportation — what he called “ghost-like action at a distance” — can transfer information between locations without actually moving the physical matter it holds.
This technology could fundamentally change the way data travels from place to place. It is based on more than a century of research related to quantum mechanics, an area of physics that controls the subatomic realm and behaves differently from anything we experience in our daily lives. Quantum teleportation not only moves data between quantum computers, but it does so in such a way that no one can intercept it.
“This means not only that the quantum computer can solve your problem, but it also doesn’t know what the problem is,” said Tracy Eleanor Northup, a researcher at the Institute for Experimental Physics at the University of Innsbruck who also studies quantum teleportation. “It doesn’t work like that today. Google knows what you are running on its servers.”
A quantum computer takes advantage of the strange ways some objects behave when they’re very small (like an electron or a particle of light) or very cold (like an exotic metal cooled to near absolute zero, or minus 460 degrees Fahrenheit). In these situations, a single object can behave like two separate objects at the same time.
Traditional computers perform calculations by processing “bits” of information, with each bit containing a 1 or a 0. Taking advantage of the strange behavior of quantum mechanics, a quantum bit or qubit can store a combination of 1 and 0 – sort of like how a spinning coin offers the tantalizing possibility that it will pop up heads or tails if it ends up flat on the table. fall.
This means that two qubits can hold four values at once, three qubits eight, four qubits 16 and so on. As the number of qubits grows, a quantum computer becomes exponentially more powerful.
Researchers believe that these devices could one day accelerate the creation of new drugs, accelerate advances in artificial intelligence and, in summary, crack the encryption that protects computers essential to national security. Around the world, governments, academic labs, start-ups and tech giants are spending billions of dollars exploring the technology.
In 2019, Google announced that its machine had achieved what scientists call “quantum supremacy,” meaning it could perform an experimental task impossible with traditional computers. But most experts believe that it will take – at the very least – several more years before a quantum computer can actually do something useful that you can’t do with another machine.
Part of the challenge is that a qubit breaks, or “decohers”, when you read information from it – it becomes a regular bit that can only hold a 0 or a 1, but not both. But by stringing together many qubits and developing ways to guard against decoherence, scientists hope to build machines that are both powerful and practical.
Ultimately, these would ideally be merged into networks that can transmit information between nodes so that they can be used anywhere, much like cloud computing services from Google and Amazon today make processing power widely accessible.
But this comes with its own problems. Partly because of decoherence, quantum information cannot simply be copied and sent over a traditional network. Quantum teleportation offers an alternative.
While it can’t move objects from place to place, it can move information using a quantum property called “entanglement”: a change in the state of one quantum system immediately affects the state of another, faraway system.
“After entanglement, you can no longer describe these states individually,” said Dr. northup. “Basically, it is now one system.”
These entangled systems can be electrons, light particles or other objects. In the Netherlands, Dr Hanson and his team used a so-called nitrogen vacancy center — a small void in a synthetic diamond in which electrons can be trapped.
The team built three of these quantum systems, named Alice, Bob and Charlie, and connected them in line with strands of optical fibers. The scientists could then entangle these systems by sending individual photons – particles of light – between them.
First, the researchers entangled two electrons — one from Alice, the other from Bob. In fact, the electrons got the same spin and so they joined or entangled in a common quantum state, each storing the same information: some combination of 1 and 0.
The researchers could then transfer this quantum state to another qubit, a carbon core, in Bob’s synthetic diamond. This released Bob’s electron, and researchers were then able to entangle it with another of Charlie’s electrons.
By performing a specific quantum operation on both of Bob’s qubits — the electron and the carbon nucleus — the researchers were able to glue the two entanglements together: Alice plus Bob glued to Bob plus Charlie.
The result: Alice got entangled in Charlie, allowing data to teleport to all three nodes.
When data travels this way, without actually traveling the distance between the nodes, it cannot be lost. “Information can be entered on one side of the connection and then appear on the other,” said Dr. Hanson.
The information cannot be intercepted either. A future quantum internet, powered by quantum teleportation, could provide a new kind of encryption that is theoretically unbreakable.
In the new experiment, the network nodes weren’t that far apart — only about 60 feet. But previous experiments have shown that quantum systems can become entangled over greater distances.
The hope is that, after several more years of research, quantum teleportation over many miles will be viable. “We’re now trying to do this outside of the lab,” said Dr. Hanson.