Entanglement "on demand" sets the stage for quantum internet

With more sensitive data than ever being shared – and stolen – online, more secure connections are desperately needed. The answer could be a quantum internet, where information is passed almost instantaneously between nodes that have been quantum entangled and are therefore physically unhackable, since any unauthorized observation of the data will scramble it. Researchers at Delft University of Technology have now overcome a major hurdle on the road towards that goal by generating quantum links faster than they deteriorate.

Quantum entanglement is a strange phenomenon where two particles become so intertwined that by looking at the state of one you can accurately infer the state of the other, no matter how large a distance separates them. This communication is effectively instantaneous, which appears to violate fundamental laws of classical physics – namely, information can't travel faster than the speed of light. Albert Einstein himself was famously unnerved by the implications, once describing it as "spooky action at a distance."

But that spookiness has been demonstrated in experiments time and time again, and scientists are beginning to harness the phenomenon for ultra-fast, ultra-secure communication networks. Last year the Micius satellite smashed the quantum entanglement distance record, transmitting information as far as 1,200 km (746 mi), and earlier this year scientists used Micius to send quantum-encrypted data between China and Austria.

In order to build a practical quantum internet though, entanglements between two particles need to be generated quickly and last long enough to pass the information onto a third node. In the new study, the researchers at TU Delft say they've finally managed to create quantum links "on demand," faster than they are lost.

The team has made several strides over the years. In 2014, they were able to teleport information across a room for the first time, and that distance was stretched to 1.3 km (0.8 mi) the following year. But as impressive as that sounds, stability and longevity were still issues.

"In 2015 we managed to establish a connection once an hour, while the connection only remained active for a fraction of a second," says Ronald Hanson, lead researcher on the project. "It was impossible to add a third node, let alone multiple nodes, to the network."

In the new study, the researchers were able to improve that ratio by several orders of magnitude. The connections still only lasted a fraction of a second, but rather than only being able to establish them once an hour, the team managed to make them 40 times per second. Crucially, that gives the information time to move to another node before the initial connection is lost, which was a major hurdle in developing a useful quantum network.

To achieve this result, the researchers used a new method to entangle two electrons housed on diamond chips, and kept 2 m (6.6 ft) apart. They also developed a new way to protect the entanglement, since any outside interference could affect the outcome.

The system is now apparently always ready for "entanglement on demand," the team says, thanks to smart quality checks that have been added to the process. In future, the researchers plan to scale the technology up to create a quantum network with multiple nodes.

"Just like in the current internet, we always want to be online, the system has to entangle on each request," says Hanson. "In 2020, we want to connect four cities in the Netherlands via quantum entanglement. This will be the very first quantum internet in the world."

The research was published in the journal Nature.

Source: Delft University of Technology