New research identifies quantum discord as a resource that can be tapped to extract information with the right quantum tools. This is an artist's illustration of the 'unlocking' of discord. Credit: Timothy Yeo / CQT, National University of Singapore

Researcher Helen Chrzanowski operates an experiment at the Australian National University that unlocks quantum discord in pairs of laser beams. Credit: The Australian National University

New research lends hope that a phenomenon called quantum discord could be harnessed to bring quantum technologies within easier reach than expected. The work, by an international team, is published 5 August in Nature Physics.

Up until a few years ago, researchers thought that realising quantum technologies would mean harnessing the most difficult-to-tame properties of the quantum world. For example, 'entanglement', the phenomenon referred to by Einstein as spooky-action-at-a-distance, was thought to be a resource required to run a quantum computer. This presents a challenge. In a laboratory setting, entanglement can be protected with near ideal conditions. Outside the lab, however, entanglement is fragile and transient.

But now researchers realise that entanglement may not always be necessary. In the past few years, scientists have discovered examples of technologies that seem to gain a quantum advantage without entanglement. Researchers are left with the question, where does the quantum power come from?

The new research by the National University of Singapore (NUS), The Australian National University (ANU), the University of Queensland and the University of Oxford identifies that quantum discord, a more robust and easy to access phenomenon than entanglement, can also deliver a quantum advantage.

The team in Singapore discovered a direct link between quantum power and quantum discord. "We've shown that quantum discord is a resource that we can tap with the right quantum tools," said Mile Gu, a Research Fellow of the Centre for Quantum Technologies at NUS.

The ANU team encoded information onto laser light to demonstrate the unlocking of this quantum resource. In their experiment, they show that they can retrieve more information by using quantum discord than if the discord is not accessed.

Ping Koy Lam, Professor at ANU, said "The experiment is analogous to decoding music from a AM/FM radio simulcast that is badly affected by static."

They found that discord is similar to shared quantum static and that more 'music' can be extracted from this simulcast with the right quantum tools. Quantum discord has been shown to be present in many systems, and might previously have been characterised as unwanted noise. This has made some scientists sceptical that it could be useful. The new results suggest otherwise. The experiment demonstrated isn't considered a quantum computation, but it shows that discord has potential that can be unlocked for quantum technologies.

Researchers are now looking for other tasks that may be enhanced by quantum discord. The hope is that discord could prove an easier path to future quantum technologies than entanglement. With a scientist's caution, Lam said "Our work hints towards the possibility that the requirements on certain quantum technologies could be relaxed."

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M. Gu et al, "Observing the operational significance of discord consumption", Nature Physics, doi:10.1038/NPHYS2376. http://dx.doi.org/10.1038/NPHYS2376

A preprint is available at arXiv:1203.0011. http://arxiv.org/abs/1203.0011

Centre for Quantum Technologies at the National University of Singapore: http://www.quantumlah.org