The discovery could allow ultra-secure encryption over fibre optic cables
The discovery could allow ultra-secure encryption over fibre optic cables
27 October 2016

A video of the Canadian prime minister explaining quantum technology’s exciting future went viral this year, and now Australian physicists are making that future a present-day reality.

The University of Queensland’s Professor Timothy Ralph, PhD student Josephine Dias and colleagues at the Centre for Quantum Computation and Communication Technology (CQC2T) have announced a discovery that could allow ultra-secure encryption over fibre optic cables.

The CQC2T was established in 2011 and was this year awarded $24.7 million in Australian Research Council funding for seven years, administered through the University of NSW.

Professor Ralph said CQC2T was the world's largest team undertaking fundamental research to create a universal quantum computing and communication ecosystem.

A “noiseless optical amplifier” was at the heart of the new research.

“When the amplification is good enough, we can split a light beam into several copies, or clones,” he said.

“This allows us to clone the light beam with minimal distortion, so that it can still be read with exquisite precision.”

Team leader ANU’s Professor Ping Koy Lam said one obstacle to sending quantum information was that the quantum state degraded before reaching its destination.

“Our cloner has many possible applications, and could help overcome this problem to achieve secure long-distance communication,” he said.

Professor Ralph said the laws of physics – in particular the ‘No Cloning Theorem’ – prevented high-quality clones being produced with a 100 per cent success rate.

The team used a “probabilistic” method to demonstrate that it is possible to produce clones that exceed theoretical quality limits.

“Imagine Olympic archers being able to choose the shots that land closest to the target’s centre to increase their average score,” Professor Ralph said.

“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.”

ANU PhD researcher Jing Yan Haw said the probabilistic method was used in many crypto-communication situations, such as generating secret keys.

“Our probabilistic cloning method generates higher quality quantum clones than have ever been made before, with a success rate of about five per cent,” he said.

“We can now create up to five clones of a single quantum state.

“We first encode information on to a light beam. Because this information is in a fragile quantum state, it is difficult to observe or measure.”

Professor Lam said quantum cloning opened up important experimental possibilities as well as having applications in ultra-secure long distance quantum networks.

“One of the problems with quantum encryption is its limited communication range,” he said.

“We hope this technology could be used to extend the range of communication, and one day lead to impenetrable privacy between two communicating parties.”

The research is published today in Nature Communications.

Media: Professor Timothy Ralph, +61 7 3346 9693; Kristin O'Connell,, +61 2 9385 7551.