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From Santa Barbara, California, to Hefei, China, scientists are developing a new breed of computer that will make 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 handle thousands of years ago. In the fall of 2019, Google unveiled an experimental quantum computer showing that this is possible. Two years later, a lab in China did the same.
But quantum computing won’t reach its potential without the help of another technological breakthrough. Call it a “quantum internet” – a computer network that can send quantum information between distant machines.
At Delft University of Technology in the Netherlands, a team of physicists has taken a significant step towards this computer network of the future, using a technique called quantum teleportation to send data across three physical locations. Previously, this was possible with just two.
The new experiment shows that scientists can extend a quantum network across an ever-increasing number of locations. “We’re now building small quantum networks in the lab,” said Ronald Hanson, the Delft-based physicist who leads the team. “But the idea is to eventually build a quantum internet.”
Their research, presented in an article published this week in the science journal Nature, demonstrates the power of a phenomenon Albert Einstein once thought impossible. Quantum teleportation – what he called “creepy action at a distance” – can transmit information between places without actually moving the physical matter that contains it.
This technology could fundamentally change the way data is transmitted from place to place. It draws on more than a century of research into quantum mechanics, a field of physics that dominates the subatomic realm and behaves unlike anything we experience in our daily lives. Quantum teleportation not only moves data between quantum computers, but also in such a way that nobody can intercept it.
“Not only does this mean that the quantum computer can solve your problem, but also that it doesn’t know what the problem is,” says Tracy Eleanor Northup, a researcher at the Institute for Experimental Physics at the University of Innsbruck, who also studies quantum teleportation. “That’s no longer possible today. Google knows what you are running on its servers.”
A quantum computer takes advantage of the strange behavior of some objects when they are very small (like an electron or a particle of light) or very cold (like an exotic metal cooled to almost absolute zero, or minus 460 degrees Fahrenheit). In these situations, a single object can behave like two separate objects at the same time.
Conventional computers perform calculations by processing “bits” of information, each bit containing either a 1 or a 0. By harnessing the odd behavior of quantum mechanics, a quantum bit, or qubit, can store a combination of 1s and 0s – a little bit like how a spinning coin has the tantalizing possibility that it will show either heads or tails when it finally falls flat on the surface table falls.
That means two qubits can hold four values at a time, three qubits eight, four 16, and so on. As the number of qubits increases, a quantum computer becomes exponentially more powerful.
Researchers believe these devices could one day accelerate the development of new drugs, fuel advances in artificial intelligence and, in short, crack the encryption that protects computers vital to national security. Around the world, governments, academic labs, startups, and tech giants are spending billions of dollars researching the technology.
In 2019, Google announced that its machine had achieved what scientists call “quantum superiority,” meaning it can perform an experimental task that was impossible with traditional computers. But most experts believe that it will still be a few years away – at least – before a quantum computer can actually do something useful that you can’t do with any other machine.
Part of the challenge is that when you read information from a qubit, it breaks, or “decoherates”—it becomes an ordinary bit that can only hold a 0 or a 1, but not both. But by stringing together many qubits and developing methods to protect against decoherence, scientists hope to build machines that are both powerful and practical.
Ultimately, these would ideally be connected into networks that can send information between nodes so they can be used from anywhere, much like cloud computing services from Google and Amazon are making computing power universally available today.
But that brings its own problems. Partly due to decoherence, quantum information cannot simply be copied and sent over a conventional network. Quantum teleportation offers an alternative.
Although it cannot move objects from place to place, it can move information by taking advantage of a quantum property called entanglement: a change in the state of one quantum system instantaneously affects the state of another, distant system.
“After entanglement, you can no longer describe these states individually,” said Dr. Northup. “It’s basically a system now.”
These entangled systems could be electrons, light particles or other objects. In the Netherlands, Dr. Hanson and his team created what is known as a nitrogen vacancy center – a tiny empty space in a synthetic diamond where electrons can be trapped.
The team built three of these quantum systems, named Alice, Bob and Charlie, and connected them in a line with strands of fiber optics. The scientists could then entangle these systems by sending single photons – particles of light – back and forth between them.
First, the researchers entangled two electrons — one belonged to Alice and the other to Bob. In fact, the electrons were given the same spin and thus became linked or entangled in a common quantum state, each storing the same information: a specific combination of 1s and 0s.
The researchers were then able to transfer this quantum state to another qubit, a carbon nucleus, in Bob’s synthetic diamond. This released Bob’s electron, and the researchers were then able to entangle it with another electron that belonged to Charlie.
By performing a specific quantum operation on both of Bob’s qubits – the electron and the carbon nucleus – the researchers were then able to glue the two entanglements together: Alice plus Bob glued to Bob plus Charlie.
The result: Alice was entangled with Charlie, allowing data to be teleported across all three nodes.
If data is transmitted in this way without actually traveling the distance between nodes, it cannot be lost. “Information can be fed on one side of the connection and then appear on the other side,” said Dr. Hanson.
The information cannot be intercepted either. A future quantum internet, powered by quantum teleportation, could offer a new type 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 longer distances.
The hope is that after a few more years of research, quantum teleportation over many kilometers will be feasible. “We’re now trying to do this outside of the lab,” said Dr. Hanson.
