I have done research in quantum computing, and here is what I hope is an informed answer.
It is often said that qubits as you see them in a quantum computer can exist in a "superposition" of 0 and 1. This is true, but in a more subtle way than you might first guess. Even with a classical computer with randomness, a bit can exist in a superposition of 0 and 1, in the sense that it is 0 with some probability and 1 with some probability. Just as when you roll a die and don't look at the outcome, or receive e-mail that you haven't yet read, you can view its state as a superposition of the possibilities. Now, this may sound like just flim-flam, but the fact is that this type of superposition is a kind of parallelism and that algorithms that make use of it can be faster than other algorithms. It is called randomized computation, and instead of superposition you can say that the bit is in a probabilistic state.
The difference between that and a qubit is that a qubit can have a fat set of possible superpositions with more properties. The set of probabilistic states of an ordinary bit is a line segment, because all there is a probability of 0 or 1. The set of states of a qubit is a round 3-dimensional ball. Now, probabilistic bit strings are more complicated and more interesting than just individual probabilistic bits, and the same is true of strings of qubits. If you can make qubits like this, then actually some computational tasks wouldn't be any easier than before, just as randomized algorithms don't help with all problems. But some computational problems, for example factoring numbers, have new quantum algorithms that are much faster than any known classical algorithm. It is not a matter of clock speed or Moore's law, because the first useful qubits could be fairly slow and expensive. It is only sort-of parallel computation, just as an algorithm that makes random choices is only in weak sense making all choices in parallel. But it is "randomized algorithms on steroids"; that's my favorite summary for outsiders.
Now the bad news. In order for a classical bit to be in a superposition, it has be a random choice that is secret from you. Once you look a flipped coin, the coin "collapses" to either heads for sure or tails for sure. The difference between that and a qubit is that in order for a qubit to work as one, its state has to be secret from the rest of the physical universe, not just from you. It has to be secret from wisps of air, from nearby atoms, etc. On the other hand, for qubits to be useful for a quantum computer, there has to be a way to manipulate them while keeping their state a secret. Otherwise its quantum randomness or quantum coherence is wrecked. Making qubits at all isn't easy, but it is done routinely. Making qubits that you can manipulate with quantum gates, without revealing what is in them to the physical environment, is incredibly difficult.
People don't know how to do that except in very limited toy demonstrations. But if they could do it well enough to make quantum computers, then some hard computational problems would be much easier for these computers. Others wouldn't be easier at all, and great deal is unknown about which ones can be accelerated and by how much. It would definitely have various effects on cryptography; it would break the widely used forms of public-key cryptography. But other kinds of public-key cryptography have been proposed that could be okay. Moreover quantum computing is related to the quantum key distribution technique which looks very safe, and secret-key cryptography would almost certainly still be fairly safe.
Yes, there is quantum encryption, by which if someone tries to spy on your communication, it destroys the datastream such that neither they nor you can read it.
However, the real power of quantum computing lies in that a qubit can have a superposition of 0 and 1. Big deal. However, if you have, say, eight qubits, you can now represent a superposition of all integers from 0 to 255. This lets you do some rather interesting things in polynomial instead of exponential time. Factorization of large numbers (IE, breaking RSA, etc.) is one of them.
The other factor where the word "quantum" computing is used regards an "entangled pair". Essentially if you can create an entangled pair of particles which have a physical "spin", quantum physics dictates that the spin on each electron will always be opposite.
If you could create an entangled pair and then separate them, you could use the device to transmit data without interception, by changing the spin on one of the particles. You can then create a signal which is modulated by the particle's information which is theoretically unbreakable, as you cannot know what spin was on the particles at any given time by intercepting the information in between the two signal points.
A whole lot of very interested organisations are researching this technique for secure communications.
其中一个巨大的问题是能够在 P 时间内解决 NP 难题，通过使用量子位的不确定性来本质上并行地强力解决问题。 （被删除的句子是错误的。量子计算机不能通过并行强制所有解决方案来工作，并且它们不能被认为能够解决NP完全问题多项式时间问题请参见此处 .)
There are a number of applications of quantum computing.
One huge one is the ability to solve NP-hard problems in P-time, by using the indeterminacy of qubits to essentially brute-force the problem in parallel. (The struck-out sentence is false. Quantum computers do not work by brute-forcing all solutions in parallel, and they are not believed to be able to solve NP-complete problems in polynomial time. See e.g. here.)
The superposition quantum states will collapse to a unique state when a observation happened. The current technologies of quantum annealing is apply a physical force to 2 quantum bits, the force adds constrains to qubits so when observation happened, the qubit will have higher probability to collapse to a result that we are willing to see.
I monitor recent non-peer reviewed articles on the subject, this is what I extrapolate from what I have read. a qubit, in addition to what has been said above. namely that they can hold values in superposition, they can also hold multiple bits, for example spin up/+ spin down/+ spin -/vertical , I need to abbreviate +H,-H,+V,-V Left+, LH,LV also not all of the combinations are valid and there are additional values that can be placed on the type of qubit each used similar to ram vs rom etc. photon with a wavelength, electron with a charge, photon with a charge, photon with a spin, you get the idea, some combinations are not valid and some require additional algorithms in order to pass the argument to the next variable(location where data is stored) or qubit(location of superposition of values to be returned, if you will simply because the use of wires is by necessity limited due to size and space. One of the greatest challenges is controlling or removing Q.(quantum) decoherence. This usually means isolating the system from its environment as interactions with the external world cause the system to decohere. November 2011 researchers factorised 143 using 4 qubits. that same year, D-Wave Systems announced the first commercial quantum annealer on the market by the name D-Wave One. The company claims this system uses a 128 qubit processor chipset.May 2013, Google Inc announced that it was launching the Q. AI. Lab, hopefully to boost AI. I really do Hope I didn't waste anyones time with things they already knew. If you learned something please up. As I can not yet comment, it really depends on what type of qubit you are working with to know the number of states for example the UNSW silicon Q. bit" vs a Diamond-neutron-valency or a SSD NMR Phosphorus - silicon vs Liquid NMR of the same.
发布评论
评论（6）
我对量子计算进行了研究，我希望这是一个明智的答案。
人们常说，您在量子计算机中看到的量子位可以以 0 和 1 的“叠加”形式存在。这是事实，但其方式比您最初猜测的更微妙。即使对于具有随机性的经典计算机，一个位也可以以 0 和 1 的叠加形式存在，即它以某种概率为 0，以某种概率为 1。就像当您掷骰子而不看结果或收到尚未阅读的电子邮件时，您可以将其状态视为可能性的叠加。现在，这可能听起来像是胡言乱语，但事实是这种类型的叠加是一种并行性，并且利用它的算法可以比其他算法更快。这称为随机计算，您可以说该位处于概率状态，而不是叠加。
它与量子位之间的区别在于，量子位可以具有一组具有更多属性的可能叠加。普通位的概率状态集是一条线段，因为所有概率都为 0 或 1。量子位的状态集是一个圆形的 3 维球。现在，概率位串比单个概率位更复杂、更有趣，量子位串也是如此。如果你能制造出这样的量子位，那么实际上一些计算任务不会比以前更容易，就像随机算法并不能解决所有问题一样。但一些计算问题（例如因式分解）具有比任何已知经典算法都要快得多的新量子算法。这不是时钟速度或摩尔定律的问题，因为第一个有用的量子位可能相当慢且昂贵。它只是某种并行计算，就像做出随机选择的算法只是在弱意义上并行地进行所有选择一样。但这是“类固醇的随机算法”；这是我最喜欢给局外人做的总结。
现在是坏消息。为了使经典位处于叠加状态，它必须是一个对您保密的随机选择。一旦你观察一枚翻转的硬币，硬币肯定会“塌陷”成正面或反面。它与量子位之间的区别在于，为了让量子位作为一个整体工作，它的状态必须对物理宇宙的其他部分保密，而不仅仅是对你保密。它必须对空气、附近的原子等保密。另一方面，为了使量子位对量子计算机有用，必须有一种方法来操纵它们，同时保持它们的状态保密。否则它的量子随机性或量子相干性就会被破坏。制造量子位并不容易，但这是常规操作。制造可以用量子门操纵的量子位，而不向物理环境透露其中的内容，是非常困难的。
除了非常有限的玩具演示之外，人们不知道如何做到这一点。但如果他们能够做得足够好以制造量子计算机，那么对于这些计算机来说，一些困难的计算问题就会容易得多。其他的则一点也不容易，而且哪些可以加速以及加速多少尚不清楚。它肯定会对密码学产生各种影响；它将打破广泛使用的公钥加密形式。但其他类型的公钥加密技术也已被提出，也可能没问题。此外，量子计算与看起来非常安全的量子密钥分发技术相关，并且密钥加密几乎肯定仍然相当安全。
I have done research in quantum computing, and here is what I hope is an informed answer.
It is often said that qubits as you see them in a quantum computer can exist in a "superposition" of 0 and 1. This is true, but in a more subtle way than you might first guess. Even with a classical computer with randomness, a bit can exist in a superposition of 0 and 1, in the sense that it is 0 with some probability and 1 with some probability. Just as when you roll a die and don't look at the outcome, or receive e-mail that you haven't yet read, you can view its state as a superposition of the possibilities. Now, this may sound like just flim-flam, but the fact is that this type of superposition is a kind of parallelism and that algorithms that make use of it can be faster than other algorithms. It is called randomized computation, and instead of superposition you can say that the bit is in a probabilistic state.
The difference between that and a qubit is that a qubit can have a fat set of possible superpositions with more properties. The set of probabilistic states of an ordinary bit is a line segment, because all there is a probability of 0 or 1. The set of states of a qubit is a round 3-dimensional ball. Now, probabilistic bit strings are more complicated and more interesting than just individual probabilistic bits, and the same is true of strings of qubits. If you can make qubits like this, then actually some computational tasks wouldn't be any easier than before, just as randomized algorithms don't help with all problems. But some computational problems, for example factoring numbers, have new quantum algorithms that are much faster than any known classical algorithm. It is not a matter of clock speed or Moore's law, because the first useful qubits could be fairly slow and expensive. It is only sort-of parallel computation, just as an algorithm that makes random choices is only in weak sense making all choices in parallel. But it is "randomized algorithms on steroids"; that's my favorite summary for outsiders.
Now the bad news. In order for a classical bit to be in a superposition, it has be a random choice that is secret from you. Once you look a flipped coin, the coin "collapses" to either heads for sure or tails for sure. The difference between that and a qubit is that in order for a qubit to work as one, its state has to be secret from the rest of the physical universe, not just from you. It has to be secret from wisps of air, from nearby atoms, etc. On the other hand, for qubits to be useful for a quantum computer, there has to be a way to manipulate them while keeping their state a secret. Otherwise its quantum randomness or quantum coherence is wrecked. Making qubits at all isn't easy, but it is done routinely. Making qubits that you can manipulate with quantum gates, without revealing what is in them to the physical environment, is incredibly difficult.
People don't know how to do that except in very limited toy demonstrations. But if they could do it well enough to make quantum computers, then some hard computational problems would be much easier for these computers. Others wouldn't be easier at all, and great deal is unknown about which ones can be accelerated and by how much. It would definitely have various effects on cryptography; it would break the widely used forms of public-key cryptography. But other kinds of public-key cryptography have been proposed that could be okay. Moreover quantum computing is related to the quantum key distribution technique which looks very safe, and secret-key cryptography would almost certainly still be fairly safe.
是的，有量子加密，如果有人试图监视您的通信，它会破坏数据流，使他们和您都无法读取它。
然而，量子计算的真正威力在于，一个量子位可以有 0 和 1 的叠加。这很重要。但是，如果您有 8 个量子位，您现在可以表示从 0 到 255 的所有整数的叠加。这使您可以在多项式而不是指数时间内做一些相当有趣的事情。大数分解（IE、破坏 RSA 等）就是其中之一。
Yes, there is quantum encryption, by which if someone tries to spy on your communication, it destroys the datastream such that neither they nor you can read it.
However, the real power of quantum computing lies in that a qubit can have a superposition of 0 and 1. Big deal. However, if you have, say, eight qubits, you can now represent a superposition of all integers from 0 to 255. This lets you do some rather interesting things in polynomial instead of exponential time. Factorization of large numbers (IE, breaking RSA, etc.) is one of them.
使用“量子”计算一词的另一个因素涉及“纠缠对”。本质上，如果你可以创建一对具有物理“自旋”的纠缠粒子，量子物理学表明每个电子上的自旋总是相反的。
如果你可以创建一对纠缠粒子，然后将它们分开，你就可以通过改变其中一个粒子的自旋，使用该设备来传输数据而不被拦截。然后，您可以创建一个由粒子信息调制的信号，该信号理论上是牢不可破的，因为您无法通过拦截两个信号点之间的信息来知道在任何给定时间粒子上的自旋。
许多非常感兴趣的组织正在研究这种安全通信技术。
The other factor where the word "quantum" computing is used regards an "entangled pair". Essentially if you can create an entangled pair of particles which have a physical "spin", quantum physics dictates that the spin on each electron will always be opposite.
If you could create an entangled pair and then separate them, you could use the device to transmit data without interception, by changing the spin on one of the particles. You can then create a signal which is modulated by the particle's information which is theoretically unbreakable, as you cannot know what spin was on the particles at any given time by intercepting the information in between the two signal points.
A whole lot of very interested organisations are researching this technique for secure communications.
量子计算有许多应用。
其中一个巨大的问题是能够在 P 时间内解决 NP 难题，通过使用量子位的不确定性来本质上并行地强力解决问题。（被删除的句子是错误的。量子计算机不能通过并行强制所有解决方案来工作，并且它们不能被认为能够解决NP完全问题多项式时间问题请参见此处 .)
There are a number of applications of quantum computing.
One huge one is the ability to solve NP-hard problems in P-time, by using the indeterminacy of qubits to essentially brute-force the problem in parallel.(The struck-out sentence is false. Quantum computers do not work by brute-forcing all solutions in parallel, and they are not believed to be able to solve NP-complete problems in polynomial time. See e.g. here.)
只是根据 Greg Kuperberg 的回答对量子计算行业进行了更新：
D-Wave 2 系统正在使用量子退火。
当发生
观察时，叠加量子态将塌陷到一个独特的状态。目前的量子退火技术是对2个量子位施加物理力，该力对量子位增加了约束，因此当观察发生时，量子位将有更高的概率塌陷到我们愿意看到的结果。参考：
Just a update of quantum computing industry base on Greg Kuperberg's answer:
D-Wave 2 System is using quantum annealing.
The superposition quantum states will collapse to a unique state when a
observationhappened. The current technologies of quantum annealing is apply a physical force to 2 quantum bits, the force adds constrains to qubits so when observation happened, the qubit will have higher probability to collapse to a result that we are willing to see.Reference:
我关注最近关于该主题的非同行评审文章，这是我从所读内容中推断出来的。除了上面所说的之外，还有一个量子位。即它们可以保存叠加的值，它们还可以保存多个位，例如 spin up/+ spin down/+ spin -/vertical ，我需要缩写为 +H,-H,+V,-V Left+, LH, LV 也并非所有组合都有效，并且可以在量子位类型上放置其他值
每个都类似于 ram 与 rom 等。具有波长的光子、带电荷的电子、带电荷的光子、带自旋的光子，你明白了，有些组合是无效的，有些组合需要额外的算法才能通过参数到下一个变量（存储数据的位置）或量子位（要返回的值的叠加位置，如果您愿意的话，只是因为电线的使用由于尺寸和空间而必然受到限制。最大的挑战之一是控制或消除 Q.（量子）退相干。这通常意味着将系统与其环境隔离，因为与外部世界的相互作用会导致系统退相干。同年，D-Wave Systems 宣布了第一个商用量子比特。该公司声称该系统使用 128 量子位处理器芯片组。2013 年 5 月，谷歌公司宣布将推出 Q.AI 实验室，希望能够推动人工智能的发展。希望我没有把任何人的时间浪费在他们已经知道的事情上。如果你学到了一些东西，请向上。
由于我还无法发表评论，这实际上取决于您使用哪种类型的量子位来了解状态数，例如 UNSW 硅 Q.bit" 与钻石中子价或 SSD NMR 磷 - 硅与液体NMR 相同。
I monitor recent non-peer reviewed articles on the subject, this is what I extrapolate from what I have read. a qubit, in addition to what has been said above. namely that they can hold values in superposition, they can also hold multiple bits, for example spin up/+ spin down/+ spin -/vertical , I need to abbreviate +H,-H,+V,-V Left+, LH,LV also not all of the combinations are valid and there are additional values that can be placed on the type of qubit
each used similar to ram vs rom etc. photon with a wavelength, electron with a charge, photon with a charge, photon with a spin, you get the idea, some combinations are not valid and some require additional algorithms in order to pass the argument to the next variable(location where data is stored) or qubit(location of superposition of values to be returned, if you will simply because the use of wires is by necessity limited due to size and space. One of the greatest challenges is controlling or removing Q.(quantum) decoherence. This usually means isolating the system from its environment as interactions with the external world cause the system to decohere. November 2011 researchers factorised 143 using 4 qubits. that same year, D-Wave Systems announced the first commercial quantum annealer on the market by the name D-Wave One. The company claims this system uses a 128 qubit processor chipset.May 2013, Google Inc announced that it was launching the Q. AI. Lab, hopefully to boost AI. I really do Hope I didn't waste anyones time with things they already knew. If you learned something please up.
As I can not yet comment, it really depends on what type of qubit you are working with to know the number of states for example the UNSW silicon Q. bit" vs a Diamond-neutron-valency or a SSD NMR Phosphorus - silicon vs Liquid NMR of the same.