本期经济学人杂志【Leaders】板块关注了谷歌宣称其开发的量子计算机在特定实验中实现了“量子霸权” (注一)，其超算能力达到了传统计算机远远无法企及的高度。由于量子计算机刚出来不久，目前它的实用价值有限。但无论如何，谷歌在量子领域的这次成功是一个重要的"Sputnik Moment" (卫星时刻，注二)，将为量子计算机以后的发展注入信心。
1981 年美国物理学家理查德费曼提出可以通过干扰量子机制来创造新型量子计算机处理难题，它的运算能力将比传统计算机强很多。最近谷歌利用一台 53 量子比特的量子计算机实现了传统架构计算机无法完成的任务，在世界第一超算需要计算 1 万年的实验中，谷歌的量子计算机只用了 3 分 20 秒。
但根据许多理论论文，量子计算机并不是在任何领域都远远强于传统计算机，实际上在许多任务上它们能带来的提升很小。在一些问题上，如果研究人员能够设计出美妙的程序和算法，那这将开发出量子计算机的强大运算潜能。
量子计算机的强大运算能力可能能够很快解密被加密的算法，这给网络安全等加密工作带来了挑战。文章最后认为，虽然目前而言量子计算机能做的看似仍有限，但谷歌的这一成功给未来量子计算机的应用注入了信心。
注释 & 配图
注一: 量子霸权（Quantum Supremacy）是指量子计算在某些任务上拥有超越所有传统计算机的计算超强能力。
注二：Sputnik Moment: 1957 年 10 月 4 日，前苏联的第一颗人造卫星叫醒了美国，美国开始全力以赴造卫星，美国人把那一天称为"Sputnik Moment" (卫星时刻)。
Google claims to have demonstrated “quantum supremacy”
Quantum computing
Google claims to have demonstrated “quantum supremacy”
It could be the field’s Sputnik moment
Print edition | Leaders
Sep 28th 2019
“Nature isn’t classical, dammit, and if you want to make a simulation of nature you’d better make it quantum mechanical, and by golly, it’s a wonderful problem because it doesn’t look easy.” With those words, in 1981, Richard Feynman, an American physicist, introduced the idea that, by harnessing quantum mechanics, it might be possible to build a new kind of computer, capable of tackling problems that would cause a run-of-the-mill machine to choke. Feynman was right: it has not been easy. Over the past four decades quantum computers have slowly evolved from squiggles on theoreticians’ blackboards to small machines in university laboratories to research projects run by some of the world’s biggest companies.
Now one of those machines, built by researchers at Google, has at last shown what all the fuss is about. It appears to have performed, in just over three minutes, a task that, the researchers estimate, the world’s most powerful classical supercomputer would take around 10,000 years to complete. Google’s machine is a special-purpose device that was designed to solve a contrived problem with few practical uses. But this display of so-called “quantum supremacy” is nonetheless a milestone (see article).
What might quantum computing actually be used for? That question is obscured by the piles of money and hyperbole that surround it. Along with 5g and ai, it is one of the technologies that presidents, of both countries and companies, love to cite. China and America have pledged to invest billions of dollars in it. There is excited talk of a race, and of the riches and power that await the first to seize the “Holy Grail of computing”.
Despite the breathlessness, quantum computers are not magical. A rich body of theoretical work proves that they will be potent, but limited. For all the talk of supremacy, quantum computers are not superior in every regard to their classical cousins. Indeed for many tasks they will offer little improvement. Yet for some problems—but only some—clever programmers or mathematicians can create algorithms that exploit the machines’ quantum capabilities. In those special cases, quantum computers offer huge gains, crunching tasks that would otherwise take years or millennia down to minutes or seconds.
Several of these algorithms have been developed. They offer a glimpse of where quantum computers might excel. In encryption, for example, a quantum machine could quickly untangle the complex maths that underlies much of the scrambling that protects information online. A world with powerful quantum computers, in other words, is one in which much of today’s cyber-security unravels. Tech firms and governments are investigating new foundations for encryption that are not known to be susceptible to quantum computers. But deploying them will be the work of decades.
As Feynman pointed out, classical computers struggle to simulate the quantum-mechanical processes that underpin physics and chemistry. Quantum computers could do so with aplomb, a useful trick for developing everything from pharmaceuticals to petrochemicals. Their ability to solve optimisation problems could help financial firms improve their trading algorithms. Artificial-intelligence researchers hope that quantum computers could offer a boost to their algorithms, too.
For now, though, all that lies in the future. Google’s machine is best thought of as a Sputnik moment. By itself, Sputnik did nothing but orbit Earth while beeping. But it proved a concept, and grabbed the world’s attention. Google’s accomplishment is one in the eye for quantum-computing sceptics. It strongly suggests the promise of quantum technology can be realised in practice as well as theory. And it will draw even more money and attention to a red-hot field. A great deal of engineering work remains before quantum computers can be used for real-world tasks. But that day has suddenly got closer. ■
This article appeared in the Leaders section of the print edition under the headline"Supreme achievement"
Print edition | Leaders
Sep 28th 2019
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