From < One qubit at a time> 摘自《经济学人》 May 4th 2006

COMPUTING¹ is about to hit a problem. （1）In each new generation the components² are smaller than they were in its predecessor³, and the speed at which this miniaturisation is happening means that within 15 years or so a fundamental limit will be reached.At that point, not only will the strange effects of quantum mechanics hold sway, the components themselves will be on the scale of atoms and no further size-reduction will be possible. Which is why scientists and engineers are seeking new ways of building computers.

One route they are exploring, which was discussed at a meeting held recently at the Royal Society in London, is called quantum computing. Instead of trying to overcome quantum weirdness⁴, this technique embraces and exploits it. （2）The thing that distinguishes a quantum computer from the sort in use today is the number of calculations it can do in parallel.Both sorts of computer use binary⁵ arithmetic, but they do so in rather different ways. A classical computer employs bits—binary digits⁶, either zero or one—to process and store information. But a bit must be one or the other; it cannot be both at the same time. A quantum computer does not suffer from this restriction⁷.

new words

miniaturisation    n. 小型化
小贴士： Quantum Computer 量子计算机

量子计算机是一种机器，像猜想的那样，基于亚原子级的微粒行为执行运算。这样的计算机，一旦被开发出来，能够比以前的计算机每秒多执行数百万条指令(MIPS)。处理能的指数级提高是由于数据单元在量子计算机中，可以同时存在几种状态，这一点与二进制计算机不同。某种意义上，机器可同时进行几个思维的思考，各种思维虽然同时产生于同样的颗粒集，但他们之间是相互独立的。

工程师发明了术语qubit来表示量子计算机的基本数据单元。一个qubit实质上是一个位（二进制数字），它可以同时呈现一个或多个值。这个理论和量子机制理论同样奇怪，在这个理论中单独的微粒可以存在于多个位置上。一种考虑qubit可以同时存在于多个状态的方式是设想它有多个面或维，每一个面或维都可以高（罗辑1）或低（罗辑0）。因此如果一个qubit有两个面，它就有四个同时存在的独立状态（00、01、10、11）；如果它有三个面，就有八个可能的状态，二机制表示为000直到111，依次类推。

量子计算机在以下应用中是非常有用的：

◆破获密码　 　◆统计分析　　 ◆大数相乘　　 ◆在理论物理学中解决问题
◆解决许多变量的最优化问题　

研究开发工程师所遇到的主要困难是要使微粒在一定的时间内以恰当的方式动作是极其难得。最轻微的干扰将使机器停止量子方式的工作转而工作在传统模式下。扩散的电磁场，物理移动，甚至极小的电子干扰都将打乱处理进程。