Now, researchers have realised that entanglement may not always be necessary, and new examples of technologies that can gain a quantum advantage without entanglement have been discovered over the past few years.
A new study, published in the journalNature Physics, from researchers in Australia, Singapore and the United Kingdom, has focused on a technology called quantum discord. This phenomenon, far more robust and easily accessible than entanglement, can also deliver a quantum advantage: it could be harnessed to bring quantum technologies within easier reach than expected.
But where does quantum discord get its quantum power from? That was the question the international team set out to answer, and their findings show that a direct link exists between quantum power and quantum discord.
One of the study authors, Mile Gu from the National University of Singapore (NUS), commented: "We've shown that quantum discord is a resource that we can tap with the right quantum tools."
By encoding information onto laser light to demonstrate the unlocking of this quantum resource, they showed that it is possible to retrieve more information by using quantum discord than by not accessing the discord.
Another study author, Ping Koy Lam from the Australian National University (ANU), likened their experiment 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, making some scientists sceptical about its potential usefulness, but these new findings suggest otherwise. The experiment carried out 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 could be enhanced by quantum discord. The hope is that discord could prove an easier path to future quantum technologies than entanglement.
Ping Koy Lam underlined that their study "hints towards the possibility that the requirements on certain quantum technologies could be relaxed".
Another study published in the same edition ofNature Physicsalso shows that less demanding resources can be used for quantum information science.
This study involved researchers from Austria, Singapore and the United Kingdom, and received two bouts of EU support.
One came from the Q-ESSENCE ("Quantum interfaces, sensors and communication based on entanglement") project, which was funded to the tune of 4.7 million euro under the ICT ("Information and communication technologies") Theme of the EU's Seventh Framework Programme (FP7). Q-ESSENCE, which runs until 2013, brings together researchers from Australia, Austria, Denmark, Germany, Italy, the Netherlands, Poland, Slovakia, Spain, Switzerland and the United Kingdom.
Support also came from a 1.75 million euro European Research Council (ERC) Advanced Grant awarded to one of the study authors, Anton Zeilinger from the University of Vienna, for his QIT4QAD ("Photonic quantum information technology and the foundations of quantum physics in higher dimensions") project.