什么是 QBit？我多久可以获得一台量子计算机？
我多久可以得到一台量子计算机？ 有什么方法可以构建一个简单的吗？ 对于早期采用者来说，它们还有多少年的时间？
我想从高层次上了解 QBit 是什么，它可以有多少种状态，以及什么类型的算法在这个领域可以很好地工作。
How soon can I get a quantum computer? Is there any way to build a simple one? How many years out are they for early early adopters?
I'd like to understand from a high level what a QBit is, how many states it can have, and what types of algorithms will work well in this arena.
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在过去的一两年里，人们对量子计算机进行了大量的炒作，但在它们变得实用之前，还有许多问题需要解决。
其中一些“只是”工程问题，例如将尺寸从房间大小的 6 量子位系统缩小到更像集成电路的密度。 或者找出一种方法来防止热噪声扰乱系统，而不需要客户手头保留大量液氮（或氦气！）。
另一方面，构建具有大量量子位的量子计算机似乎存在一些更基本的问题。
其中最主要的是纠错。 用于量子计算的纠缠系统的部分固有性质是它们可能会自发地失去“相干性”。 在增加纠缠寿命方面已经取得了长足的进步，但您可以可靠执行的操作数量仍然非常有限。
量子计算中的一些纠错技术已经开发出来，但我读到的关于量子 EC 的上一篇文章表明，所需的纠错 qbit 数量或多或少与活动 qbit 数量呈对数增长。 请注意，初始常数因子可能非常大 - 可能需要 5 个物理 qbit 来表示 1 个逻辑 qbit。
在某种程度上（具体程度还有待观察），这种规模的增长将削弱量子计算相对于传统计算在速度上的指数优势。
好的，现在您可以得到一个 6 qbit 系统，它太小了，无法解决“有趣”的问题。 像对 2048 位数字进行因式分解这样的事情将需要具有数百万或数十亿量子位的系统。 当然，您会“立即”得到答案，但是使用当前技术没有明确的途径可以达到接近该性能水平。 仅将问题加载到系统中可能会超过相干寿命。
哦，回答你的其他问题：
我认为大多数人都在使用具有一对状态的量子存储系统。 原则上，大多数这些系统可以在每个存储单元存储多个不重叠的状态，但我认为更多的努力是为了让设备可靠地工作，而不是最大化效率。
量子算法和量子物理学一样很奇怪。 这里没有试图解释它们是如何工作的，而是一篇关于 Shor 整数因式分解算法的文章。
http://en.wikipedia.org/wiki/Shor's_algorithm
这是一个纠错问题参考：
http://en.wikipedia.org/wiki/Quantum_error_ Correction
There's been a good deal of hype about quantum computers over the last decade or two, but there a number of problems that will need to be resolved before they'll become practical.
Some of these are "just" engineering problems, like shrinking the size down from room-sized 6-qbit systems to something more like the density of an integrated circuit. Or figuring out a way to prevent thermal noise from scrambling the system, without requiring the customer to keep large stocks of liquid Nitrogen (or Helium!) on hand.
On the other hand, there appear to be some more fundamental problems with constructing quantum computers with large numbers of qbits.
Primary among these is error-correction. Part of the inherent nature of the entangled systems used for quantum computing is that they can lose "coherence" spontaneously. Great strides have been made in increasing the entangled lifetime, but you're still very limited in the number of operations that you can perform reliably.
Some techniques for error correction in quantum computations have been developed, but the last article I read on quantum EC indicated that the number of error-correcting qbits required goes up more-or-less logarithmically with the number of active qbits. Note that the initial constant factor may be quite large - it can take 5 physical qbits to represent 1 logical qbit.
To some extent (it remains to be seen how much), this growth in size is going to mitigate against the exponential advantage in speed that quantum computation is supposed to have over conventional computation.
Okay, so you can get a 6 qbit system today, which is way too small to tackle "interesting" problems with. Something like factoring a 2048-digit number is going to require systems with millions or billions of qbits. Sure, you'll get the answer "instantly", but there's no clear path to get anywhere near that level of performance using current techniques. Just loading the problem into the system would probably exceed the coherence lifetime.
Oh, to answer your other questions:
I think that most folks are working with quantum storage systems with a single pair of states. In principle, most of these systems could store multiple non-overlapping states per storage unit, but I think a lot more effort is going into making the equipment work reliably at all, rather than maximizing efficiency.
Quantum algorithms are weird in the same way that quantum physics is. Rather than trying to explain how they work, here's an article on Shor's algorithm for factoring integers.
http://en.wikipedia.org/wiki/Shor's_algorithm
And here's a reference on the error-correction issue:
http://en.wikipedia.org/wiki/Quantum_error_correction
量子计算机在相当长的时间内不会问世。 没有简单的方法来构建一个。
Qubit
Quantum computers will not be coming out for quite a long time. There is no easy way to build one.
Qubit
我想说他们已经来了。 :)
第一台“工作”的 3 量子位 NMR 量子计算机建于 1998 年。该领域仍处于起步阶段，几乎所有进展仍然是理论上的，并且仅限于学术界，但在 2007 年，一家名为 D-Wave Systems 的公司展示了原型工作中的 16 量子位，以及今年晚些时候的 28 量子位绝热量子计算机。 他们的努力引人注目，因为他们声称他们的技术在商业上可行且可扩展。 截至 2010 年，他们拥有 7 个钻机，当前一代芯片拥有 128 个量子位。 他们似乎与谷歌合作寻找有趣的问题来测试他们的硬件。
我推荐这段 24 分钟的短视频和有关 D-Wave 的维基百科文章可提供快速概述，此博客由 D-Wave 创始人兼首席财务官撰写。
I'd say they're already here. :)
The first "working" 3-qubit NMR quantum computer was built in 1998. The field is still in infancy, and almost all progress is still theoretical and confined to academia, but in 2007 a company called D-Wave Systems presented a prototype of a working 16-qubit, and later during the year 28-qubit adiabatic quantum computer. Their effort is notable since they claim that their technology is commercially viable and scalable. As of 2010, they have 7 rigs, current generation of their chips has 128 qubits. They seem to have partnered with Google to find interesting problems to test their hardware on.
I recommend this short 24-minute video and Wikipedia article on D-Wave for a quick overview, and there a lot more resources on this blog written by D-Wave founder and CFO.