Surprising Quantum Source Yields Info Advantage

Quantum entanglement may not always be necessary to run quantum computers, new research suggests. Moreover, technologies discovered over the past few years can gain a quantum advantage without entanglement.

Until recently, researchers thought that realizing quantum technologies would mean harnessing the most difficult-to-tame properties of the quantum world, such as entanglement. This phenomenon, referred to by Einstein as "spooky action at a distance," can be protected under near-ideal conditions in the lab; elsewhere, however, entanglement is fragile and transient.

Now, scientists from the National University of Singapore (NUS), the Australian National University (ANU), the University of Queensland and the University of Oxford have discovered that entanglement may not always be necessary. Examples of technologies that seem to gain a quantum advantage without entanglement have been observed, leaving researchers to question the source of quantum power.

New research identifies quantum discord as a resource that can be tapped to extract information. Here, researcher Helen Chrzanowski operates an experiment at the Australian National University that unlocks quantum discord in pairs of laser beams. (Image: The Australian National University)

The answer may lie in quantum discord, a more robust and easy-to-access phenomenon than entanglement. Shown to be present in many systems, discord was characterized previously as unwanted noise, making some scientists skeptical that it could be useful. Results of a new experiment, however, suggest otherwise.

The Singapore scientists 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 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 accessing quantum discord than by not accessing it.

Although the international team demonstrated that discord can be unlocked for quantum technologies, they said the experiment is not considered a quantum computation.

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

Researchers hope that discord could be an easier path to future quantum technologies than entanglement. This is an artist’s illustration of the “unlocking” of discord. (Image: Timothy Yeo/CQT, National University of Singapore)

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.

The team is now looking for other tasks that may be enhanced by quantum discord. The hope is that discord could be an easier path to future quantum technologies than entanglement.

“Our work hints towards the possibility that the requirements on certain quantum technologies could be relaxed,” Lam said.

The work appeared in the Aug. 5 issue of Nature Physics.

For more information, visit: www.nus.edu.sg