Reverend AtheiStar Posted November 26, 2006 Share Posted November 26, 2006 http://www.world-science.net/othernews/061...um-computer.htm A step toward quantum computers Nov. 22, 2006 Courtesy University of Utah and World Science staff Physicists say they’ve taken a step toward building computers that work at blinding speeds thanks to the weird realities of quantum physics, the science of subatomic particles. Physicist Christoph Boehme works with equipment that he uses to show the feasibility of a quantum computer's reading data stored in the form of atomic "spins." (Courtesy John Lupton, U. of Utah) -------------------------------------------------------------------------------- In a study to appear in the December issue of the research journal Nature Physics, they claim to show the possibility of reading data stored in the form of the “spins” of atoms. These spins “can be measured by very subtle electric currents passing through,” said the University of Utah’s Christoph Boehme, one of the researchers. This resolves “a major obstacle for building a particular kind of quantum computer,” called the phosphorus-and-silicon type, he added. The problem involves how to get the computer to read data. Many roadblocks remain, he cautioned. “If you want to compare the development of quantum computers with classical computers, we probably would be just before the discovery of the abacus.” Modern computers contain transistors, electrical switches that store data in pieces called bits. A bit is a chunk of information consisting of either a 0 or a 1, representing either no electrical charge, or some charge, respectively. A computer with three bits thus contains eight possible combinations of the two digits: 111, 011, 101, 110, 000, 100, 010 and 001. Three bits in an ordinary, digital computer can store only one of those eight groups at a time. Quantum computers would be based on the strange principles of quantum mechanics, in which the smallest particles can be in different places at the same time. In a quantum computer, one “qubit,” or quantum bit, could be 0 and 1 simultaneously. So with three qubits, the device could store all eight combinations at once, and calculate eight times faster than a three-bit digital computer. With more bits, the quantum computer’s advantage grows exponentially. A quantum computer with 64 qubits would be faster by 2 to the 64th power, or about 18 billion billion times, than a typical personal computer. A question is how to physically represent the 0s and 1s in a quantum computer. One approach is to encode this as the “spins” of the nuclei, or cores, of atoms. Subatomic particles have a property known as spin, which is akin, though not identical, to actual spinning: in short, they can act somewhat as though they were spinning. Scientists infer this from the fact that they act as tiny magnets, and also are electrically charged. A moving charge creates a magnetic field according to certain rules. For subatomic particles, a spinning motion can account for the measured magnetic fields. The calculations show that particles can spin in two opposite directions, termed “up” and “down.” The reason actual spinning isn’t believed to occur is that if it did, at the speed required, parts of the particle’s surface would move faster than light. That would violate Einstein’s well-established Theory of Relativity. In a spin-based quantum computer, down and up spins would represent 0 and 1. One qubit could have a both values simultaneously. Boehme’s study follows a quantum computing strategy proposed in 1998 by Australian physicist Bruce Kane. In such a computer, phosphorus atoms would be sprinkled into a stick of silicon, the semiconductor used in digital computer chips. The goal is to keep phosphorus atoms from being too close together, which would let them interact in a way that disrupts the information. Data would be encoded in the spins of those atoms’ nuclei. Externally applied electric fields could serve to read the spins. In this way, Boehme and colleagues wrote that they were able to read the combined spin of 10,000 of the nuclei and electrons—charge-carrying particles—of phosphorus atoms near the silicon’s surface. A real computer would need to read the spins of single particles, not thousands. But past efforts, based on a technique called magnetic resonance, were able to read only the combined spins of the electrons of 10 billion phosphorus atoms, Boehme said. So the new work represents a million-fold improvement, and shows single spins are readable in principle—though it would take another 10,000-fold improvement, Boehme argues. But the study’s point, he added, is that it shows one can electrically “read” data stored as not only electron spins but as the more stable spins of nuclei. The researchers used a sliver of silicon crystal about three times the width of a human hair. The nuclear spin of one phosphorus atom would store one qubit. The scientists then allowed a tiny electrical current to run through the device. The current’s exact size would depend on the spin direction of the phosphorus electrons. That gives “a readout of phosphorus electron spins,” which in turn also reveals the spins of the nuclei, since the two have a known relationship, Boehme said. Link to comment Share on other sites More sharing options...
Sexton Blake Posted December 15, 2006 Share Posted December 15, 2006 The trouble with such super computers is that they are too small. A stray cosmic ray, an emmission from a nearby atom or similar and you get a hugely wrong answer. Though the Voyager computers were antiques by today's standards, they did the job whereas today's far smaller computers probably would not have as cosmic radiation would have made endless "ghosts in the machines", ruining their efficiency and accuracy. Link to comment Share on other sites More sharing options...
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