Quantum information has been sent from one side of a simple quantum network to the other, passing through an intermediate network node without affecting it
25 May 2022
A quantum network can teleport information between unconnected nodes using so-called quantum entanglement – an important step towards building a super-secure quantum internet.
Objects that share a quantum entanglement have linked properties. Entanglement is central to proposals for a quantum internet, which could greatly improve privacy compared with current internet systems. One idea is to build a network of connected quantum bits, or qubits, which are entangled with qubits elsewhere in the network rather than with the neighbouring nodes they are directly linked with. But entanglement of these network qubits has so far only been demonstrated with directly connected qubits.
Ronald Hanson at Delft University of Technology in the Netherlands and his colleagues built a simple network containing a number of diamond-based qubits arranged into three nodes, dubbed Alice, Bob and Charlie. There was no direct connection between Alice and Charlie, only an indirect link each shared with Bob. But Alice and Charlie shared a quantum entanglement, which means it is impossible to measure information from one of them without changing the state of the other.
When Charlie’s quantum state was changed, Alice’s state also changed, meaning information “teleported” across Bob without passing through it.
“It’s really teleportation as in science-fiction movies,” says Hanson. “The state, or information, really disappears on one side and appears on the other side, and because it’s not travelling the space in between, [the data] can also not get lost.”
Though using entanglement in this way had been theoretically possible for decades, it was only successfully demonstrated here because the qubits at the nodes include “memory” qubits, which can hold quantum states for longer time periods than standard qubits.
Building a quantum internet network doesn’t offer any increases in speed over a conventional system, even though two nodes in the network change at the same instant. This is because users sharing information about changes to the network must do so through traditional, non-quantum communication. But a quantum web does offer truly private functions, such as eavesdropping-proof communication or data servers that can never discover the source of data they are crunching. “There’s also probably lots of [applications] that we still have to find out,” says Hanson.
While Hanson and his team is the first to build and test a quantum network in which non-neighbouring nodes are entangled, other teams have been experimenting with different kinds of quantum communication, such as those that use entangled photons.
“Trying these types of experiments on different platforms is very important,” says Charles Adams at Durham University, UK. “We don’t know yet which technology is [going to succeed] – maybe it will be some kind of hybrid of different technologies.”
Journal reference: Nature, DOI: 10.1038/s41586-022-04697-y
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