I.B.M. Researchers Inch Toward Quantum Computer

Published: February 28, 2012

I.B.M. is jumping into an area of computing that has, until now, been primarily the province of academia: the quest to build a quantum computer.

A computer that took advantage of the oddities of quantum physics could solve in seconds certain problems that would occupy present-day computers for billions of years. But for now, it is impossible to build such a computer because the bits of information it would need for the calculations fall apart before a calculation can be completed. The problem is, in essence, like trying to knit a sweater with yarn that unravels before the first purl.

On Tuesday, I.B.M. researchers will present experimental results that they say put them close to solving this problem, both by lengthening the lifetime of the quantum bits of information and by quickening the pace of computation. The presentation will take place at a meeting of the American Physical Society in Boston.

“In the past, people have said, maybe it’s 50 years away, it’s a dream, maybe it’ll happen sometime,” said Mark B. Ketchen, manager of the physics of information group at I.B.M.’s Thomas J. Watson Research Center in Yorktown Heights, N.Y. “I used to think it was 50. Now I’m thinking like it’s 15 or a little more. It’s within reach. It’s within our lifetime. It’s going to happen.”

Many university researchers have done good work solving the basic science problems, Dr. Ketchen said, but “it’s going take an I.B.M. in the end to put it together.”

It’s still too early for I.B.M. to have a commercial product in mind, but computer scientists are encouraged that the company is paying attention.

Scott Aaronson, a professor of electrical engineering and computer science at the Massachusetts Institute of Technology, called I.B.M.’s work “a cause for cautious optimism” in the development of quantum computers.

“It looks very interesting,” Dr. Aaronson said of the I.B.M. research. “Basically, it’s another step in continuing progress.”

While a working quantum computer is still quite a few years away, there have been a number of advances over the last couple of years, and the I.B.M. one is just among the most recent. These days, the path to the future now looks more like a series of very hard engineering problems rather than an uphill fight against physics.

Current computers perform their calculations using 1’s and 0’s, with each binary digit called a “bit” of information. In quantum mechanics, multiple possibilities exist at once, and a quantum bit — qubit, for short — is not necessarily a “1” or a “0” but a combination of both. By stringing together qubits, a quantum computer could perform a multitude of calculations simultaneously.

For certain problems like searching databases or factoring very large numbers — the basis of today’s encryption techniques — quantum computers could produce an answer in days or maybe even seconds, whereas the fastest conventional computer would take longer than 13.7 billion years.

The I.B.M. researchers are building quantum computer components out of electronic circuits containing superconductors, materials that carry electricity without electrical resistance. When cooled to a hundredth of a degree above absolute zero, the circuits act as qubits.

The problem is that a qubit becomes scrambled in short order, and the information it carries turns into gibberish. When physicists started experiments a little more than a decade ago, a qubit lasted only a few billionths of a second. (An alternate approach, trapping ions in electric and magnetic fields, can produce longer-lived qubits. But the superconducting circuit approach takes advantage of current computer chip technologies.)

In the latest I.B.M. results, which build on a technique developed by Robert J. Schoelkopf, a physics professor at Yale, a qubit lasted as long as one-10,000th of a second.

Even though that is still not long enough for perfect calculations, it is almost good enough for error correction algorithms to detect and fix any mistakes. “We’re just crossing this threshold,” Dr. Ketchen said, “which is a big morale booster that says, gee, this is becoming doable.”

Below the threshold, generating reliable answers is impossible. “No matter how many qubits you had, you couldn’t even get one effectively good one because of the error rates being too high,” he said.

The progress is promising enough that it is time to start thinking about related challenges, such as how to program a quantum computer or how to extract the answer that a quantum computer has calculated.

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