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Quantum number crunching
By Laurie Ann Toupin, Contributing Editor -- Design News, October 7, 2002
Quantum computing has long been the fodder of science fiction novels. Mark Eriksson, a University of Wisconsin-Madison physics professor, hopes to make the concept the basis for non-fiction papers instead. He and his associates have developed a type of "quantum dot" device for holding electrons that can be scaled up to build a working quantum computer. Each quantum dot device contains just one electron. When the devices are aligned, the electrons they house become usable quantum bits, or qubits, for computing. The design incorporates a "back-gate" that serves as an electron reservoir, a quantum well that confines electrons vertically, and split "top gates" that provide lateral confinement by electrostatic repulsion. "The novel feature of our design," says Eriksson, "is the combined use of vertical tunnel coupling through the back gate, together with lateral coupling defined by the split top gates." To load a single electron into a dot, the gate potentials are adjusted so that single-electron filling is energetically favored. Unlike the bits of classical, serial computers, which exist in either the 0 or 1 state, qubits can exist in more than one state at once. This elusive quality of their components frees quantum computers to calculate all the possible solutions to a problem simultaneously, instead of running through them one-by-one like their slower, serial counterparts. This ability to parallel process means quantum computers hold tremendous number-crunching potential for certain tasks — such as highly sophisticated data encryption and code-breaking — that now defy even the most powerful computers. The group is in the beginning stages. "People often talk about quantum computing in the future tense, but that's not really right — it exists today. People have solved simple problems with it, but in the future we want to address problems that can't be solved by any other means," says Eriksson. For more information, contact Mark Eriksson either by phone (608) 263-2689 or e-mail maeriksson@facstaff.wisc.edu.
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