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Rise of the photon clones: New method could lead to 'impenetrable' comms

New tech aims to boost security and range of quantum cryptography

By Katyanna Quach, 26 Oct 2016

Physicists have produced "near-perfect" clones of quantum information that can be used to send and retrieve information securely over long distances through quantum cryptography.

Research into using quantum mechanics for cryptography reasons is a bustling area. More countries are beginning to invest in technology that could enable perfectly secure communication.

China launched the world's first quantum science satellite earlier this year to test how information could be encoded into entangled photons that were blasted into space and sent back.

A big problem, however, is that over those long distances quantum information can degrade. The photons carrying the information can be bounced around and absorbed into the fibre-optic cables or the atmosphere, destroying the quality of information and causing errors.

Cloning the quantum information can unravel the hidden information in the photons in a better, more readable state. But the success rate can never be 100 per cent.

The "no-cloning theorem" states that it is impossible to create an identical copy of an unknown quantum state. When the photons are entangled, the quantum states of each photon can not be individually defined and cannot be cloned perfectly.

A paper published in Nature Communications on Wednesday shows that a team of scientists have created a "probabilistic method" that demonstrates it is possible to create quantum information clones to a higher degree – beyond the theoretical limit.

First a beam of photons is amplified using a noiseless optical amplifier and then split to create clones of the original photons.

Explaining the probabilistic method is tricky business. To visualise the method, Professor Timothy Ralph, a researcher at the Centre for Quantum Computation and Communication Technology at the University of Queensland, said to think of archery.

"Imagine Olympic archers being able to choose the shots that land closest to the target's centre to increase their average score. By designing our experiment to have probabilistic outputs, we sometimes 'get lucky' and recover more information than is possible using existing deterministic cloning methods. We use the results closest to a 'bullseye' and discard the rest," Ralph said.

The success rate is 5 per cent and each photon can be cloned five times, Jing Yan Haw, lead author of the study and PhD researcher at the Australian National University (ANU), said.

The cloning method could be useful for generating secret keys that can encrypt and decrypt sensitive information.

"One of the problems with quantum encryption is its limited communication range. We hope this technology could be used to extend the range of communication, and one day lead to impenetrable privacy between two communicating parties," said Professor Ping Koy Lam, co-author of the paper and quantum optics researcher at ANU. ®

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