An international research team, led by the scientists at University of Bristol, claims to have developed a prototype city-wide quantum network, which could be used to send completely secure and unhackable messages over the internet.
The researchers say their prototype is the largest-ever quantum network of its kind, with the potential to serve millions of people by enabling them to share encryption keys for their messages.
Quantum communication systems are considered to be more secure than conventional networks as they rely on the quantum properties of photons, rather than computer code that can be cracked by hackers. However, such systems are very complex and expensive to make.
In the current study, Dr Siddarth Joshi and his colleagues used a multiplexing entanglement technique to create a new type of quantum network.
Quantum entanglement is a phenomenon in which two particles become indistinguishably linked. Whatever happens to one particle instantly affects the other, irrespective of the distance between them.
Entanglement can be used to create encrypted communications channels that are secured against hacking due to the laws of quantum physics.
Scientists have developed a form of secure encryption, known as quantum key distribution, in which transmitted photons carry information. The technique allows two users to share a secret key to encrypt and decrypt the information, without the risk of interception. However, this method is effective only for two users, rather than a network.
Earlier this year, a Chinese research team claimed they had smashed the previous record for maintaining two quantum memories in an entangled state at maximum distance. The researchers said they were able to realise entanglement of two quantum memories over 22km of field-deployed fibres via a two-photon interference.
In the multiplexing entanglement technique used by the University of Bristol scientists, the light particles emitted by a single central source (and carrying information) are split so multiple users can receive them efficiently. This eliminates the need to replicate the whole communication system.
According to Joshi, the team has tested the network in both the lab and on existing optical fibres across Bristol. The network included eight users (nodes), the most distant of which were located 17km apart.
"Besides being completely secure, the beauty of this new technique is its streamlined agility, which requires minimal hardware because it integrates with existing technology," Joshi said.
While previous quantum systems have taken several years to complete build, this prototype network was built within months at a cost of less than £300,000.
The researchers claim that their quantum network can expand in size without an unreasonable increase in the costs.
"We have proved the concept and by further refining our multiplexing methods to optimise and share resources in the network, we could be looking at serving not just hundreds or thousands, but potentially millions of users in the not too distant future," Dr Joshi noted.
The detailed findings of the study have been published in journal Science Advances.
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