1st June 2014
A breakthrough in quantum teleportation
Scientists have transferred data by quantum teleportation over a distance of 10 feet with zero percent error rate.
Teleporting people through space, as done in Star Trek, is impossible with our current knowledge of physics. Teleporting information is another matter, however, thanks to the extraordinary world of quantum mechanics. Researchers at Delft University of Technology in the Netherlands have succeeded in transferring the information contained in a qubit – the quantum equivalent of a classical bit – to a different quantum bit over a distance of three metres (10 feet), without the information having travelled through the intervening space. This was achieved with a zero percent error rate.
The breakthrough is a vital step towards a future quantum network for communication between ultra-fast quantum computers – a "quantum internet". Quantum computers will solve many important problems that even today's best supercomputers are unable to tackle. Furthermore, a quantum internet will enable completely secure information transfer, as eavesdropping will be fundamentally impossible in such a network. To achieve teleportation, researchers in this study made use of an unusual phenomenon known as entanglement.
"Entanglement is arguably the strangest and most intriguing consequence of the laws of quantum mechanics," argues the head of the research project, Prof. Ronald Hanson. "When two particles become entangled, their identities merge: their collective state is precisely determined, but the individual identity of each of the particles has disappeared. The entangled particles behave as one, even when separated by a large distance. The distance in our tests was three metres – but in theory, the particles could be on either side of the universe. Einstein didn't believe in this prediction and he called it 'spooky action at a distance'. Numerous experiments, on the other hand, agree with the existence of entanglement."
This animation shows schematically how to teleport the state of a spin between two distant locations.
Using entanglement as a means of communication has been achieved in previous work by scientists – but the error rates have been so high as to make those methods impractical for real-world applications. In this new effort, Hanson has solved the error rate problem, bringing it down to zero. His team is the first to have succeeded in teleporting information accurately between qubits in different computer chips: "The unique thing about our method is that the teleportation is guaranteed to work 100%," he says. "The information will always reach its destination, so to speak. And, moreover, it also has the potential of being 100% accurate."
Hanson's team produce solid-state qubits using electrons in diamonds at very low temperatures and shooting them with lasers: "We use diamonds because 'mini prisons' for electrons are formed in this material whenever a nitrogen atom is located in the position of one of the carbon atoms. The fact that we're able to view these miniature prisons individually makes it possible to study and verify an individual electron and even a single atomic nucleus. We're able to set the spin (rotational direction) of these particles in a predetermined state, verify this spin and subsequently read out the data. We do all this in a material that can be used to make chips out of. This is important, as many believe that only chip-based systems can be scaled up to a practical technology," he explains.
Hanson plans to repeat the experiment this summer over a much larger distance of 1300m (4265 ft), using chips located in various buildings on the university campus. This experiment could be the first that meets the criteria of the "loophole-free Bell test", and could provide the ultimate evidence to disprove Einstein's rejection of entanglement. Various groups, including Hanson's, are currently striving to be the first to realise a loophole-free Bell test – considered the Holy Grail within quantum mechanics.
The results of this study are published this week in Science.