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Australia enters the quantum communications race


Physicists at Australian National University (ANU) and University of Queensland (UQ) have produced near-perfect clones of quantum information using a new method to surpass previous cloning limits.

A global race is on to use quantum physics for ultra-secure encryption over long distances, with China, the US and Canada making strides.

Now Australia has entered the bid with a new cloning method that uses high-performance optical amplifiers to clone light encoded with quantum information. According to the physicists, this method could enable the implementation of quantum encryption using existing fibre optic infrastructure.

“One obstacle to sending quantum information is that the quantum state degrades before reaching its destination. Our cloner has many possible applications, and could help overcome this problem to achieve secure long distance communication,” said ANU Professor Lam.

Currently, the record distance for transferring a quantum state by teleportation is six kilometres, and is held by Canadian and US researchers.

The laws of physics (in particular the ‘No Cloning Theorem’) prevent high quality clones from being produced with a 100 per cent success rate.

The Australian team, led by Lam, uses 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,” said UQ Professor Timothy Ralph, whose research team initially proposed the method.

“By designing our experiment to have probabilistic outputs, we sometimes ‘get lucky’ and recover more information than is possible using deterministic cloning methods. We use the results closest to a ‘bullseye’ and discard the rest.”

This probabilistic method is used in many aspects of encrypted communication, 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. We can now create up to five clones of a single quantum state,” said ANU researcher Jing Yan Haw.

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

“At the heart of the demonstration is a ‘noiseless optical amplifier’,” said Ralph.

“When the amplification is good enough, we can then split a light beam into clones. ‘Amplify-then-split’ allows us to clone the light beam with minimal distortion, so that it can still be read with exquisite precision.”

The researchers hope the method could be used to extend communication ranges and eventually lead to hack-proof communications.


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