Quantum cryptography to tighten secure information

New protocols using quantum cryptography that ensure data can be carried reliably and securely across longer distances have been designed. 

Engineers at the University of Toronto have devised the first all-photonic repeaters that exploit the laws of quantum mechanics to transmit information from one use to another, coded in the quantum states of photons.

The new protocol advances international quantum communication networks over existing optical infrastructure making communications more secure.

Traditionally, more than 90 per cent of photons are lost over distances greater than 50km when sent, limiting the range of quantum communication. Researchers have focused in recent years on developing quantum repeaters to extend that range and give photons a boost, thus reducing loss.

However, the repeaters acted much like mini quantum computers, storing the entangled photons and transmitting their signals down the fibres, but at low repeat rates that made them inconvenient and slow.

The newly devised all-photonic quantum repeaters transmit protons over long distances using photons only, without the demanding requirements of matter quantum memories or an interface between matter and light at all.

Professor Hoi-Kwong Lo, researcher at the University of Toronto, said: “There's a lot of interest in the community around designing a quantum Internet that will be more information-rich and more powerful, but these quantum states can also be fragile.

“Our motivation was to design a means for communicating securely and reliably over long distances.”

According to the researchers the proposed all-photonic repeaters boast higher quantum-communication rates, use optical elements whose proof-of principle demonstrations have already been made and function at room temperature.

All-photonic repeaters could be used to chain individual quantum computers securely, which although of interest to researchers worldwide are far from being patented anytime soon.

“Imagine in the future we have various quantum computers around the world, run by different users,” said Professor Lo. “We would want to convey information between them, but current modes of communication are not safe against attacks or losses.”

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