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In 1981 the physicist Richard Feynman speculated about the possibility of “tiny computers obeying quantum mechanical laws.” He suggested that such a quantum computer might be the best way to simulate real-world quantum systems, a challenge that today is largely beyond the calculating power of even the fastest supercomputers.
Since then there has been sporadic progress in building this kind of computer. The experiments to date, however, have largely yielded only systems that seek to demonstrate that the principle is sound. They offer a tantalizing peek at the possibility of future supercomputing power, but only the slimmest results.
Recent progress, however, has renewed enthusiasm for finding avenues to build significantly more powerful quantum computers. Laboratory efforts in the United States and in Europe are under way using a number of technologies.
Significantly, I.B.M. has reconstituted what had recently been a relatively low-level research effort in quantum computing. I.B.M. is responding to advances made in the past year at Yale University and the University of California, Santa Barbara, that suggest the possibility of quantum computing based on standard microelectronics manufacturing technologies. Both groups layer a superconducting material, either rhenium or niobium, on a semiconductor surface, which when cooled to near absolute zero exhibits quantum behavior.
The company has assembled a large research group at its Thomas J. Watson Research Center in Yorktown Heights, N.Y., that includes alumni from the Santa Barbara and Yale laboratories and has now begun a five-year research project.
“I.B.M. is quite interested in taking up the physics which these other groups have been pioneering,” said David DiVincenzo, an I.B.M physicist and research manager.
Researchers at Santa Barbara and Yale also said that they expect to make further incremental progress in 2011 and in the next several years. At the most basic level, quantum computers are composed of quantum bits, or qubits, rather than the traditional bits that are the basic unit of digital computers. Classic computers are built with transistors that can be in either an “on” or an “off” state, representing either a 1 or a 0. A qubit, which can be constructed in different ways, can represent 1 and 0 states simultaneously. This quality is called superposition.
The potential power of quantum computing comes from the possibility of performing a mathematical operation on both states simultaneously. In a two-qubit system it would be possible to compute on four values at once, in a three-qubit system on eight at once, in a four-qubit system on 16, and so on. As the number of qubits increases, potential processing power increases exponentially.
