量子计算：平行宇宙的神奇机器还是被夸大的科技神话？

如果大家是科普爱好者，一定知道有两样东西是我们人类看似已经可以触及，但还没有取得成功的，一旦成功，就会让人类文明升级的两大法宝。一个就是可控核聚变，另一个就是量子计算。

可控核聚变就不用说了，永远都是“还有20到30年就能够实现”，从我们小时候开始就这么说，到现在还是需要“20到30年”。另一个就是量子计算了，几乎每隔一段时间都要爆出一个大新闻，谷歌、微软、亚马逊等公司抢着发布自己的量子计算芯片，抬升股价，但一旦进入实际使用阶段，还非常遥远。

量子计算给人类的承诺更是还要超过可控核聚变，动不动就是“秒杀了现在的经典计算机”，一个经典计算机要计算成百上千年的任务，让量子计算机几分钟就能解决。当然，这些吹捧量子计算的科普文章大都会弱弱地提醒一下，并不是所有的任务都能得到加速。而且一个流传甚广的说法是，现有的量子算法来看，量子计算最主要的应用就是破解现有的加密。比如坊间传闻，只要量子计算机研发成功，比特币的安全机制就会瞬间失效，比特币就会跌得一文不值。事实真的如此吗？

五一期间，有关著名的数学科普大V3Blue1Brown（3B1B）推出了一个介绍量子计算的视频，终于把量子计算的一些细节降低到了像我这种水平能够大概看懂的程度。其实最好的欺骗或者最好的忽悠并不是撒谎，而是只说出一部分真相。而很多关于量子计算的科普文章就是这样的，他只告诉了你部分关于量子计算的背景知识，而忽略了其他细节，代之以一些似是而非的表述，从而神话了这一概念。

比如我看到一个脑洞大开关于量子计算原理的解释是，量子计算之所以能够如此高效快速地完成计算任务，是因为他将这些任务分包给了量子叠加态形成的平行宇宙，仿佛量子计算机就是一个可以联通平行宇宙的神奇机器。量子力学的多世界平行宇宙诠释只是量子力学诸多诠释中的一种，说实话，刚了解的时候，觉得这个想法真的是脑洞大开，但是如果深入了解量子科学、量子力学之后，你很难相信平行世界的方式理解量子力学，同样会有很多难以解释的地方，他很难是真的。

事实上，如果从相对纯数学一点的角度来理解量子计算，他其实并没有那么神秘，特别是在与图形结合并可视化之后，这正是3Blue1Brown这个频道所擅长的，他将复杂的数学概念通过动画的方式，以可视化的形式展现出来，变得非常容易理解。

今天先聊到这里，先说一部分结论，那就是量子计算的加速效果，在大多数情况下，并没有像宣传的那么神奇。

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If you are a science popularization enthusiast, you must know that there are two things that we humans seem to have reached but have not yet succeeded in. Once successful, they will be the two magic weapons that will upgrade human civilization. One is controlled nuclear fusion, and the other is quantum computing.

Controlled nuclear fusion needs no introduction. It has always been said that "it will be achieved in 20 to 30 years", since we were kids. Even now, it still takes "20 to 30 years". Another one is quantum computing. Almost every once in a while, a big news story breaks out. Companies like Google, Microsoft, and Amazon rush to release their own quantum computing chips to boost their stock prices. However, once it enters the practical application stage, it is still very far away.

The promise quantum computing makes to humanity even exceeds that of controlled nuclear fusion. It often claims to "outperform today's classical computers in an instant". Tasks that a classical computer would need to calculate for hundreds or even thousands of years can be accomplished by a quantum computer in just a few minutes. Of course, most of these popular science articles that praise quantum computing will weakly remind us that not all tasks can be accelerated. Moreover, a widely circulated claim is that, from the perspective of existing quantum algorithms, the main application of quantum computing is to crack existing encryption. For instance, there is a rumor in the market that as long as the quantum computer is successfully developed, the security mechanism of Bitcoin will instantly fail and Bitcoin will drop to nothing. Is that really the case?

During the May Day holiday, the well-known mathematics popular science platform V3Blue1Brown (3B1B) released a video introducing quantum computing, finally reducing some details of quantum computing to a level that I, at my level, could roughly understand. In fact, the best deception or the best deception is not lying, but only revealing part of the truth. Many popular science articles about quantum computing are like this. They only tell you part of the background knowledge about quantum computing and ignore other details, replacing them with some ambiguous expressions, thus mythologizing this concept.

For instance, I came across an imaginative explanation of the principle of quantum computing, which states that the reason why quantum computing can complete computing tasks so efficiently and rapidly is that it subcontracts these tasks to the parallel universes formed by quantum superposition states, as if the quantum computer were a magical machine capable of connecting parallel universes. The multi-world parallel universe interpretation of quantum mechanics is just one of the many interpretations of quantum mechanics. To be honest, when I first learned about it, I thought this idea was really imaginative. But once you delve deeper into quantum science and quantum mechanics, it's hard to believe that the parallel world approach to understanding quantum mechanics is also very difficult to explain, and it's hard to be true.

In fact, if we understand quantum computing from a relatively pure mathematical perspective, it is not that mysterious, especially when combined with graphics and visualized. This is precisely what the 3Blue1Brown channel is good at. It presents complex mathematical concepts in a visual form through animation, making them very easy to understand.

That's all for today. Let's start with a part of the conclusion, which is that the acceleration effect of quantum computing, in most cases, is not as magical as advertised.