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>  News Releases >   2007 >   July

Dartmouth scientist contributes to research that could aid quantum computing

Dartmouth College Office of Public Affairs • Press Release
Posted 07/31/07 • Rebecca Bailey • (603) 646-3661

Yeong-Ah Soh
Yeong-Ah Soh, associate professor of physics and astronomy (Photo by Joseph Mehling '69)

An international team that includes a Dartmouth physicist has reported findings that could advance the emerging field of quantum information processing. The team's findings, reported July 26, 2007, in the online version of the magazine Science, shed light on how to detect and manipulate the direction of electron spins, one potential medium for recording data in a quantum computer.

Titled "Mesoscopic Phase Coherence in a Quantum Spin Fluid," the paper "is a collaboration between groups that have worked together very productively over a long period of time," said Yeong-Ah Soh, Dartmouth associate professor of physics and astronomy. "The research was successful due to a combination of factors—namely a good idea, high-quality samples, intensive measurements at state-of-the-art international facilities supported by in-house measurements, and, ultimately, good physical insights."

First proposed in the 1970s, quantum computing employs certain quantum physical properties of atoms or nuclei as the "quantum bits," or "qubits," of the computer's processor and memory. Unlike today's computer bits, which exist as either 0s or 1s, qubits have an infinite choice of values, meaning they can potentially perform multiple operations simultaneously and solve problems beyond the scope of today's computers.

Quantum physical properties that have been explored for use as qubits include various properties of photons and ions; the size or energy state of an electron's orbit around an atom; and the direction of electron spins, the approach studied by Soh and her colleagues.

The team used powerful imaging technology in the United Kingdom and the United States to analyze Japanese-produced samples of a ceramic composed of chains of nickel-centered oxygen octahedra. This material is known as a "spin liquid"—one in which the electron spins (analogous to tiny compasses) point in random directions, with no particular order, even at very low temperatures.

The team found that, contrary to intuition, the electron spins could achieve "quantum order" even in the spin liquid, and could do so at lengths of up to 20 nanometers, or billionths of a meter. While not much to the naked eye, this distance is significant in quantum information processing. The team also studied how they could limit or eliminate the quantum order by heating the ceramic or introducing chemical impurities.

Soh's collaborators include the paper's lead author, Guangyong Xu, of John Hopkins University and Brookhaven National Laboratory in Upton, NY; Collin L. Broholm, Ying Chen, and Michel Kenzelmann of Johns Hopkins University and the NIST Center for Neutron Research in Gaithersburg, MD; Gabriel Aeppli of the London Centre for Nanotechnology and University College London; John. F. DiTusa of Louisiana State University; Christopher D. Frost from the ISIS Facility, Rutherford Appleton Laboratory, U.K.; Toshimitsu Ito and Kunihiko Oka of the National Institute of Advanced Industrial Science and Technology (AIST), Japan; and Hidenori Takagi from AIST and University of Tokyo.

The work was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science, the National Science Foundation, a Wolfson-Royal Society Research Merit Award (UK), and by the Basic Technologies program of the UK Research Councils.

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