"In the science business you have concepts that tell you it should be this or that and when it's two things at once, that's a sign you have something interesting to find," says Jim Allen, an emeritus professor of physics at the University of Michigan. "Mysteries are always intriguing to people who do curiosity-driven research." 

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He is alluding to the properties of samarium hexaboride, a material that flummoxed science since the 1960s. Known as SmB6 for short, it was recently identified as an exotic state of matter, whose implications are fundamental in the quest to create a viable quantum computer. A revolutionary type of device that could use particles including electrons and whole atoms for processing and memory, a quantum computer would be faster than the most powerful conventional supercomputer, perform more calculations simultaneously, and be more secure.

SmB6 has within its structure a rare form of electron, called a Dirac electron. These electrons seemingly sit on the fence between classical physics (which works for big things such as atoms or galaxies) and quantum physics (which works for very small things, such quarks and other subatomic particles). It was this that piqued Allen's interest.

Dirac electrons interact more with each other than those from an outside source; externally applied electrons race across the surface of SmB6 but are blocked from interacting with the electrons underneath. SmB6 effectively conducts electricity while insulating itself; scientists call substances of this type "correlated materials," and they could drive electrons in a similar fashion to silicon in conventional computers.

"Before this, no one had found Dirac electrons in a strongly correlated material," said Lu Li, assistant professor of physics at the University of Michigan's College of Literature, Science, and the Arts. "We thought strong correlation would hurt them, but now we know it doesn't."

In lieu of the familiar 1s and 0s of binary code used in conventional computing, quantum computers used a "qubit" that can be a 1 or a 0 at the same time. However, because qubits are so small, any sort of measuring system a quantum computer would use to recognize data would force a qubit into a definite 1 or 0, which defeats the purpose of a quantum computer. Because SmB6's Dirac electrons seem to be in two words at once, they could be used with other materials to let a computer measure a qubit indirectly and keep it and its properties intact.

However, because samarium hexaboride has observed correlated properties only at extremely cold temperatures, much too cold for a practical quantum device, Li is circumspect.

"While I don't think this material is the answer," he continues, "now we know that this combination of properties is possible and we can look for other candidates." 

The findings, in an article co-authored by Li, was published in the journal Science. 

TagsDirac electron, University of Michigan, samarium hexaboride, SmB6, quantum computer