2013年5月11日 星期六

A Quantum Computer D-Wave Aces Its Test


A Quantum Computer Aces Its Test

The long-sought quantum computer, a machine potentially far ahead of today’s best supercomputers, is almost as hard to define as it is to build. For at least a few particular uses, however, the unusual computer made by D-Wave Systems now seems to be very fast indeed.

Next week a professor at Amherst College will present her findings about the performance of the D-Wave machine, which its makers say makes use of such unusual properties of quantum physics as a particle’s ability to move in one direction and its opposite at the same time.

The professor, Catherine C. McGeoch, who is the Beitzel professor in technology and society at Amherst, gave the machine a so-called optimization problem and compared the results with those generated by  popular software from I.B.M. running on a high-performance machine.

The D-Wave machine, she said, was 3,600 times as fast as the  conventional system.
“There is no sense in which this is the definitive statement about quantum computing,” Ms. McGeoch said. “I’m more interested in how well it works, not whether or not it is quantum.”
That question matters a great deal to some others in the field. While quantum properties are among the most tested and proven domains of physics, the concepts behind them — for example, suggestions that we live in one of many universes, or that objects not in direct contact can affect each other — make such properties hard to accept.

Harnessing them for the sake of computation, suggested as a possibility more than two decades ago, has proved difficult.

The optimization problem is typically something like how a traveling salesman would plan a complicated trip most effectively. Ms. McGeoch tested three problems involving optimization. In two of them, the D-Wave computer was slightly faster. In the third, it was markedly faster.

D-Wave, which was the subject of an article in The New York Times in March, has been criticized for making claims about its quantum capabilities that cannot be supported.

Over time, however, D-Wave’s performance has improved, and the skeptics have toned down their criticism. Nonetheless, D-Wave is sensitive about the issue and, even after selling a working machine to Lockheed Martin, eager to rebut the criticism.

Ms. McGeoch, who has spent more than 25 years testing computer speeds, performed the experiments while on sabbatical and was retained by D-Wave to run the tests.

D-Wave solves optimization problems by setting them in the context of energy consumption: the lowest power needed to achieve a stated outcome, which it says is quickly achieved through a quantum process, is the answer. D-Wave thinks that many problems in computing might be restated as optimization problems and that its machine could be coupled with cloud computing systems for particularly hard problems.

Ms. McGeoch said D-Wave’s chips had performed well and might have better outcomes in the future, as its machines become more powerful, and more complex optimization problems are set.

“There could be a tipping point,” she said. “If the problems get big enough, conventional systems break down. In theory, you could solve a large number of optimization problems. People don’t know how to do that conventionally without losing a lot of efficiency.”


人們企盼已久的量子計算機有可能能把當今最厲害的超級計算機遠遠甩在身後,可是,給它下定義卻幾乎跟製造它一樣困難。不過,現在看來,至少是就一些特定用途而言,D-Wave系統公司(D-Wave Systems)打造的一台非凡的計算機的確是速度非常快。
下周,阿默斯特學院(Amherst College)的一名教授將發表她對D-Wave計算機表現的評估。製造者稱,這台機器利用了量子物理學中的非凡特性,即粒子可以同時往兩個相反的方向運動。
前述教授名為凱瑟琳·C·麥吉奧赫(Catherine C. McGeoch),是阿默斯特學院技術與社會研究的拜策爾教授,她對D-Wave計算機進行了所謂的優化問題測試,並將結果與一台高性能計算機運行常用IBM軟件所得結果進行了比較。
然而,隨着時間的推移,D-Wave的表現已經改善,懷疑者們也軟化了批評的語調。儘管如此,D-Wave對這個問題依然很敏感,即便已經向洛克希德·馬丁(Lockheed Martin)售出了一台可用於工作的電腦,它還是急於反駁批評。
D-Wave解決優化問題的方法是把問題置於能源消耗的背景之下:達到規定結果所需的最低功率即是答案,據D-Wave所說,利用量子程序,他們很 快就實現了這一點。D-Wave認為,電腦運算的許多問題都可以轉化為優化問題,而其電腦可以配合雲計算系統來處理特別棘手的問題。