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Quantum ‘dance’ could revolutionize computing


An international team of scientists has observed swarms of electrons spinning in a synchronized quantum dance within a new material.

PRINCETON (US)—For years scientists have suspected that atoms placed in certain configurations would trigger electrons to perform a quantum dance of sorts. Now an international team of scientists has observed swarms of electrons spinning in a synchronized quantum dance within a new material. They are hopeful the discovery could be harnessed to transform computing and electronics.

“We believe this discovery is not only an advancement in the fundamental physics of quantum systems but also could lead to significant advances in electronics, computing, and information science,” says team leader Zahid Hasan, an assistant professor of physics at Princeton University, who led the international collaboration that included scientists from the United States, Switzerland, and Germany.

The researchers reported witnessing the exotic behavior in a carefully constructed crystal made of an antimony alloy laced with bismuth. The coordinated behavior observed involves a strange form of rotation. Unlike most objects, which return to their original “face” when revolved full circle or 360 degrees, the harmonized electrons need to be twisted two full turns or 720 degrees in order to go back to the same face at the surface of the material.

“This quantum weirdness—a coordinated twist in the spin of electrons even though there is no magnetic field around—is what we’ve been searching for by fine tuning our experiments over the last few years,” Hasan says. “It’s a very fundamental piece of new physics—it goes beyond what you would typically learn in a quantum physics textbook. In principle, you can use this new quantum dance of electrons to construct a very bizarre electronic circuit.”

Computer designers could employ the quantum effect to construct machines with a far more subtle range of processing options than the simple “on” or “off” logic that now exists, the researchers says. The team also has been studying other materials that could produce such effects and developing sharper imaging techniques to track the finer quantum behavior.

Today’s computers employ a simple on-off logic that is based on the positive or negative charge of an electron buried in a silicon semiconductor. New designs could take advantage of a rich set of possibilities offered by the quantum spin of the electrons in the experimental material to enhance power, speed and memory.

“We can use this new quantum property of spinning particles to make computers that can store much more information and can have the capacity to perform computations much faster than present-day machines,” said David Hsieh, a graduate student in Princeton’s Department of Physics and the first author on the paper.

Until recently there was no imaging technique to detect these very subtle quantum effects. “A key breakthrough that made the discovery possible is that through an international collaboration we developed a set of methods based on X-rays to see the individual spin of electrons,” Hasan says. “We can now observe the spin by taking pictures of the north and south poles of these tiny bar magnets, which revealed this new secret of the quantum world.”

“As a technical achievement, or a series of physics achievements alone, it is pretty spectacular,” says Princeton professor Philip Anderson, a winner of the 1977 Nobel Prize in Physics. Anderson, who was not involved with the work, says the findings are both interesting and significant for theoreticians.

Quantum physics is the set of physical laws governing the realm of the ultra-small. There, objects appear to follow rules that are radically different from the world seen by the naked eye. In the quantum dominion, for example, an object can seem to be in two places at the same time, and there is no distinction between particles and waves. Quantum computers will be designed to take advantage of these properties to enrich their capacities in many ways.

In addition to electrical charge, electrons possess rotational properties. In the quantum world objects can turn in ways that are at odds with common experience. The British physicist Paul Dirac, who won the Nobel Prize in Physics in 1933, proposed that an electron’s rotation makes it behave like a tiny bar magnet with both north and south poles, a property he coined “quantum spin.”

The 720-degree rotational property in a soup of electrons seen in the current experiment was expected in theory by theoretical physicists at Princeton, the University of Pennsylvania and the University of California-Berkeley. Electrons would need to be moving at extremely high speeds in order for it to happen. But the questions became where to look and how to detect it.

The results for the research team were the culmination of years of searching for the right materials and experimental techniques. The current experiment was based on the researchers’ hunch that electrons in bismuth-laced antimony or selenium (the materials are technically known as “topological quantum spin Hall insulators”) would exhibit unusual effects because they move at high velocities that mimic the presence of a magnetic field inside the material. This would allow for the bizarre quantum motion to take place.

The researchers expect to employ the new technique to improve medical imaging technologies in studies of the fine quantum behavior of unusual magnets, superconductors, and other materials.

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