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SUMMER 2001

Team set to build next-generation computer

New superconducting material packs an applied punch

Eom joins faculty

Postdoc takes honors

Team set to build next-generation computer

Photo of quantum computer developers van der Weide, Joynt, Eriksson and Lagally

Clockwise, from top left: Professors Dan van der Weide, Bob Joynt, Mark Eriksson and Max Lagally will pool their knowledge and resources to build a semiconductor-based quantum gate or qubit. view larger image

A working quantum computer could be so powerful that it would solve in seconds certain problems that would take the fastest existing supercomputer millions of years to complete. Seeking this "Holy Grail" of computing power, an interdisciplinary team of UW-Madison engineering and physics researchers will use silicon germanium quantum dots to build the foundation — a semiconductor-based quantum gate or qubit — for a new generation of computers.

The quantum dot, a nanometer-scale "box" that holds a distinct number of electrons, is the center of the invisible atomic world of quantum computing. The number can be manipulated by changing electrical fields near the dot.

A quantum computer would use these dots to take advantage of a quantum phenomenon known as superposition, in which, for example, an electron's spin state would be both up and down at the same time. Where a classical computer uses an on or off state to represent bits of information in the "zeros" and "ones" of binary code, a quantum computer uses the superposition as qubits.

With superposition, a qubit is in neither the zero nor the one state before being measured, but exists as both zero and one simultaneously. The particle's spin state is determined at the time it is measured.

Quantum theory holds that particles that have interacted are entangled in pairs through the process of correlation, and one particle's up or down spin state affects that of its "mate." These entangled particles retain their connection no matter how great the distance between them.

All of this together means that a quantum computer could perform massively parallel calculations so that certain "hard" problems, like encryption, could be solved in mere seconds.

UW-Madison's team consists of students and faculty, including physics Professors Mark Eriksson and Bob Joynt; Professor Max Lagally, materials science and engineering; and electrical and computer engineering Professor Dan van der Weide, who is the project's principal investigator.

The team will combine advanced physics theory, silicon-germanium heterostructured materials, and low-temperature and high-frequency measurements to build an elemental piece of a quantum computer, called a solid-state Controlled-NOT logic gate.

Creating this item will be an achievement in itself; however, the team's approach also is a breakthrough. A useful quantum computer will require a chain of thousands of qubits; researchers have been limited by their inability to link many qubits.

The UW-Madison team's process uses new science and existing technology similar to complementary metal-oxide semiconductor (CMOS) technology. That means if one qubit can be made, the process likely could be scaled to make and link qubits by the thousands. The researchers predict their success could result in the first useful quantum computer in 10 to 30 years. While related research efforts might focus on theory, materials growth or experimentation alone, the UW team is situated to integrate its new approach with existing results and theory into a working result.

 

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Date last modified: Monday, 17-Jan-2011 17:46:34 CST
Date created: 20-Nov-2001 12:16:00

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