By LIDIA WASOWICZ
UPI Senior Science Writer
Published 12/19/2001 4:45 PM

SAN JOSE, Calif., Dec. 19 (UPI) -- Heading toward a new generation of computer technologies, researchers have performed the world's most complicated quantum-computer calculation yet.

Though practical quantum computers -- which will potentially pack millions or even billions of times as much processing power as the best of today's machines -- are still decades away, a leading expert described the feat as a "milestone" he did not expect would be reached for several more years.

During the 18-month experiment, scientists at IBM's Almaden Research Center in San Jose, Calif., and Stanford University in Palo Alto, Calif., took the quest for atomic-scale circuitry -- millions of times smaller than current computer microprocessors -- to a new level that may bring a step closer to reality visions of the next generation of devices once reserved for the pages of science fiction.

Whether future-world will hold such marvels as super-smart microscopic diagnostic probes that are injected into the bloodstream to seek signs of disease or infinitely powered supercomputers that need never be plugged in, as some envision, remains to be seen. The new development, detailed in the British journal Nature, points in the right direction, scientists said.

"This is one milestone on a long path to practical quantum computers," Peter Shor of AT&T Laboratories in Florham Park, N. J., a key figure in the annals of quantum computation, told United Press International.

"It is very exciting when theoretical suppositions bear out in the laboratory; this is one such time," lead study author Isaac Chuang, who conducted the work at IBM and is now associate professor at the Massachusetts Institute of Technology, said in a telephone interview. "The engineering feat is extremely significant."

"We now believe there is no experimental or theoretical problem, in principle, with the construction of quantum computers. This was unclear only a few years ago," he said.

Physicist Albert Chang of Purdue University in West Lafayette, Ind., deemed the finding "very significant" but cautioned, "it is quite a ways off to have practical implications which will impact the daily lives of the general public."

A quantum computer gets its power by taking advantage of certain quantum properties of atoms that allow them to work together as chunks of information, called quantum bits or qubits for short, that serve simultaneously as the device's processor and memory.

The team turned a billion custom-designed molecules in a test tube into a 7-qubit quantum computer that solved a simple version of a mathematical problem at the heart of many of today's data-security cryptographic systems.

"I think it's a great accomplishment -- I wasn't expecting anybody to demonstrate the (results) for several more years," Shor told UPI.

"This result reinforces the growing realization that quantum computers may someday be able to solve problems that are so complex that even the most powerful supercomputers working for millions of years can't calculate the answers," said Nabil Amer, IBM manager and strategist.

Building such machines -- no easy task -- may take 15 or 20 years or longer, scientists speculated.

"To factor cryptographically significant numbers, you are going to need thousands of quantum bits and billions of computational steps," Shor said. "You can do interesting computations with significantly less than these resources, but I can't imagine doing anything really useful without hundreds of quantum bits and tens of thousands of steps, which seems to be still many years away."

"We believe that quantum computers have capabilities that ordinary digital computers could never match. But building quantum computers will be very hard and we still don't know how to do it. We'll have to start small and build our way up, and along the way we'll learn a lot about what approaches are most promising," John Preskill, professor of theoretical physics at the California Institute of Technology in Pasadena, Calif., and founding director of the new Institute for Quantum Information, told UPI.

"For now, the best way to do a small quantum computation is to use a molecule as the computer, and to perform the computation on many molecules to make it feasible to read out the result. In their new paper, Chuang et al. have advanced the state of this art."

Proposed in the 1970s and 1980s by the likes of Nobel physics laureate Richard Feynmann of Caltech, Paul Benioff of Argonne National Laboratory in Illinois, David Deutsch of Oxford University in England and Charles Bennett of IBM, quantum computers remained little more than an academic curiosity until 1994. Then, Shor changed all that with a revolutionary experiment that pointed directly to potential "killer applications," something useful that only a quantum computer could do. The promise lay in the secret world of encryption.

The marvel of atom-sized computers is that, unlike today's bulkier ilk, they would take advantage of a strange phenomenon described by quantum theory that allows objects, such as atoms or electrons, to be in two places or to exist in two states at the same time. The benefit would be in the speed, increased to nearly unimaginable levels.

Shor showed how it could be done. He devised the first algorithm, or set of rules for solving a problem such as when multiplying numbers of playing chess, that, in principle, can efficiently figure out what numbers multiplied together constitute a given number -- no matter how large that number. While any school child can quickly determine that, for example, 10 is the product of 2 times 5, when it comes to, say, thousand-digit numbers, the computation would take more than the estimated age of the universe, scientists said.

This increasing difficulty of finding factors of ever-larger numbers underpins the security of numerous common methods of encryption. RSA, the most popular public key cryptosystem, often used to protect electronic bank accounts, provides an example.

"Shor's algorithm got everybody excited about doing quantum computing," Chuang told UPI.

Taking the next step, Chuang and colleagues designed their molecular computer that correctly identified 3 and 5 as the factors of 15.

"It was a difficult experiment and well executed. An intriguing aspect of it was that the team had to design and build their own synthetic molecule -- the computer used in the study. Possibly -- or possibly not -- that is a harbinger of future quantum technology: the need to build designer hardware, which may or may not be molecular hardware," Preskill said.

"Now we have the challenge of turning quantum computation into an engineering reality," Chuang said. "If we could perform this calculation at much larger scales -- say the thousands of qubits required to factor very large numbers -- fundamental changes would be needed in cryptography implementations."

"Although the jury is still out as to whether we will ultimately succeed in our quest to build a practical quantum computer, this work demonstrates that many key ideas are in principle workable," Chang told UPI. "It will further stimulate our imagination and lead us toward potentially dramatic breakthroughs."