Reviving Einstein's "spooky action at a distance"

18 March 2014

Physicists from the Australian National University and the University of Queensland have demonstrated a software-based quantum amplifier, which has the potential to expand the use of ultra-secure quantum cryptographic communications.

The development could lead to new ways to guarantee security of everyday communications, including financial transactions and email.

“This has the potential to guarantee security for any kind of information you want to transmit, from particularly sensitive information, like banking data or electoral results, to personal emails,” said ANU PhD researcher Helen Chrzanowski, from the Research School of Physics and Engineering.

Quantum cryptography exploits quantum mechanics to guarantee 100 per cent security between a sender and receiver of information.

Most forms of quantum communication also use a phenomenon known as quantum entanglement, which Albert Einstein described as “spooky action at a distance”.

Although powerful, this phenomenon is fragile and is often destroyed before it can be transmitted over large distances. The usual approach to combating loss - an amplifier – such as those used for radio or television signals, only makes the situation worse.

Now researchers, led by Professor Ping Koy Lam at the Research School of Physics and Engineering, have used a sophisticated scheme to work out when an amplified signal works or fails.

They have developed an algorithm which allows them to verify whether a quantum entanglement signal has been successfully received. The software allows the physicists to filter out unwanted signal failures.

That means it is now possible to use an amplifier to distribute the signals over greater distances, and for the sender and receiver to know if the signal has arrived safely.

“The results showed clear success in resurrecting the quantum effect that so perturbed Einstein,” Professor Lam said.

Professor Timothy Ralph from UQ said the results would help harness the power of quantum entanglement in communications.

“If we want to use entanglement over larger distances, and harness its power for telecommunication, we need quantum amplifiers that allow us to resurrect quantum entanglement in a communication line,” Professor Ralph said.

The results have been published in the latest on-line issue of Nature Photonics.