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Connecting indium antimonide quantum dots

Feb 27, 2013
A novel spin technique has allowed scientists to move closer to creating what they say is the first viable high-speed quantum computer
Recent research offers a new spin on using nanoscale semiconductor structures to build faster computers and electronics. Literally.

University of Pittsburgh and Delft University of Technology researchers have revealed a new method that better preserves the units necessary to power lightning-fast electronics, known as qubits (pronounced CUE-bits).

The scientists explored InSb (indium antimonide) quantum dots in their study.

Hole spins, rather than electron spins, can keep quantum bits in the same physical state up to ten times longer than before, a new report by the scientists, finds.

“Previously, our group and others have used electron spins, but the problem was that they interacted with spins of nuclei, and therefore it was difficult to preserve the alignment and control of electron spins,” says Sergey Frolov, assistant professor in the Department of Physics and Astronomy within Pitt’s Kenneth P. Dietrich School of Arts and Sciences, who did the work as a postdoctoral fellow at Delft University of Technology in the Netherlands.

Whereas normal computing bits hold mathematical values of zero or one, quantum bits live in a hazy superposition of both states. It is this quality, said Frolov, which allows them to perform multiple calculations at once, offering exponential speed over classical computers. However, maintaining the qubit’s state long enough to perform computation remains a long-standing challenge for physicists.

“To create a viable quantum computer, the demonstration of long-lived quantum bits, or qubits, is necessary,” continues Frolov. “With our work, we have gotten one step closer.”

The holes within hole spins, Frolov explains, are literally empty spaces left when electrons are taken out. Using extremely thin filaments called InSb nanowires, the researchers created a transistor-like device that could transform the electrons into holes.

They then precisely placed one hole in a nanoscale box called “a quantum dot” and controlled the spin of that hole using electric fields. This approach - featuring nanoscale size and a higher density of devices on an electronic chip - is far more advantageous than magnetic control, which has been typically employed until now, notes Frolov.

“Our research shows that holes, or empty spaces, can make better spin qubits than electrons for future quantum computers.”



Graphic displaying spin qubits within a nanowire

“Spins are the smallest magnets in our universe. Our vision for a quantum computer is to connect thousands of spins, and now we know how to control a single spin,” Frolov adds. “In the future, we’d like to scale up this concept to include multiple qubits.”

This work is further described in the paper, “Electrical control over single hole spins in nanowire quantum dots,” by V. S. Pribiag et al in Nature Nanotechnology, (2013). DOI:10.1038/nnano.2013.5

The research was supported by the Dutch Organisation for Fundamental Research on Matter, the Netherlands Organisation for Scientific Research, and the European Research Council.

Frolov and his Netherlands colleagues were recent winners of the 2012 Newcomb Cleveland Prize, an annual honour awarded to the author/s of the best research article/report appearing in Science, which is published weekly by the American Association for the Advancement of Science (AAAS).



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