Talk:Quantum circuit

why is freedman larsen wang cited here?
that article is about topological quantum computing. It is related, but only vaguely. I think it is confusing to cite here. — Preceding unsigned comment added by 82.17.71.110 (talk) 16:31, 1 June 2020 (UTC)

unconventional use of the term "qubit"
The article (at least the section "Reversible logic gates") uses the term "qubit" with a very different meaning than the one given in the qubit article (to which this article links). There it is defined as a single quantum bit, with two possible quantum states. The usage here differs in two respects; a qubit here consists of n such units, and the term is used to refer to the states themselves, not to the entity of which they are states. This is either simply wrong, or it needs to be explained.


 * Yes, you are absolutely right. The usage here is very sloppy (it is my doing, and I assume the burden of guilt). Qubit is a unit of measurement of quantum information. This sloppiness though, possibly, has some justification (I think) in the way the term bit is used to express a unit of mesurement of classical information and spaces of bitstrings. I´ll fix this up in the next few days. Thanks for pointing it out.--CSTAR 02:10, 7 Apr 2005 (UTC)


 * I don't see the analogy with bits. A bit has two possible states. You can then have a set of N bits. We have names for different Ns, like nibble, byte, Kbyte, Mbyte, etc. but a set of N bits is never called "a bit". I think just consistently using the term "n-qbit" throughout or "set of qubits" or "series of qubits" is best.  Maybe we should call 8 qubits a Qbert! --ReedHedges

Reversible logic gates
Hi, this is slightly confusing at first read: "for an AND gate one cannot generally recover the two input bits from the output bit; the case both input bits are 1 is the exception." It's more obvious for OR so maybe that would be a better example. Or, you should explain AND a bit more, perhaps like this: "For and AND gate one cannot in all cases recover the two input bits from the output bit. If the output bit is 0, the input bits could be (0, 1), (1, 0), or (0, 0) (with equal likelyhood)." You could add the OR example. At leasnt, you could de-emphasize the confusing exceptional case by putting it in paretheses. --ReedHedges

Article is confusing
Template for a confusing article added. This article does not explain to the layman what a quantum circuit is, only some boffins will understand it, and probably not many of them either. The formulas will remain unintelligible to the layman so I am not sure what the point is of having them unless they can be explained in small understandable steps. As far as I know Wikipedia is not a repository for intellectuals only, but should serve the community in general.

The page needs to explain clearly to the layman what a quantum circuit is and perhaps with some simple examples so that the features and applications of quantum circuits become comprehensible.

I would say at least half the article should focus on the layman. The introduction is especially poor, giving the layman no real clue what a quantum circuit really is but is instead a collection of jargon aimed at physicists. 190.76.28.253 (talk) 04:35, 19 November 2007 (UTC)


 * I strongly agree that the equations are of little value and a friendlier introduction would be better for everyone, scientists or not. If you are able to provide this, it would be much appreciated. Skippydo (talk) 05:58, 20 November 2007 (UTC)


 * I doubt this article could be written much more clearly without being a book length work. The author does his best to use analogies, but the simple fact is that no one who hasn't taken at least a graduate level quantum mechanics course is going to be able to thoroughly understand the concept.  Also, making this article any less confusing would involve duplicating information from several other articles that are already pretty well written, such as the articles on Quantum Computers and Qubits.  The confusing tag isn't meant to mark things that are inherently confusing, and I think this is one example of that misuse.  However, the introduction could be a bit more thorough.  Therefore, I'm removing the confusing tag and adding the technical tag to the talk page as suggested on the cleanup tags page. David.S.Hollman (talk) 15:18, 29 December 2010 (UTC)

Ell squared operator not defined
It is not clear in this context what ell squared function is (represented by the cursive l).
 * $$H_{\operatorname{QB}(n)}= \ell^2(\{0,1\}^n).$$

63.73.199.69 (talk) 21:49, 2 April 2008 (UTC)

W_CNOT) - bracket?
WCNOT) is used twice in the article. I am wondering if the closing bracket has some meaning. --mfb (talk) 22:25, 28 February 2014 (UTC)

Undefined terms?
I sort of understood this up to about half way through "Quantum Calculations", where there seem to be some undefined terms. These may be things that are obvious within the field, but links would be helpful. Examples:

> observables in quantum mechanics are usually defined in terms of projection valued measures on R;

What is R? The set of real numbers?

> Y valued observable

Does this mean an single observable consisting of Y quantities, i.e. a vector (in the mathematical rather than physical sense)?

Where is δ defined? Is the inequality intended to be the definition, and if so what is its significance?

--Scottwh (talk) 12:45, 7 November 2020 (UTC)


 * δ is a measure how good your experiment is - the smaller δ is the better. Not sure about R. --mfb (talk) 17:30, 7 November 2020 (UTC)

Worlds first quantum integrated circuit
Australia acheaved worlds 1st quantum inter grated circuit 2022.

Australian company owns world wide I.P

https://ia.acs.org.au/article/2022/world-first-quantum-integrated-circuit-made-in-australia.html 49.185.170.202 (talk) 13:37, 17 March 2023 (UTC)

"Acceleration with FPGAs"-section has issues
1) The explanations for why using FPGAs in particular are not convincing:

"FPGA is a kind of hardware that excels at executing operations in parallel, supports pipelining, has on-chip memory resources with low access latency, and offers the flexibility to reconfigure the hardware architecture on-the-fly which make it a well suited tool to handle matrix multiplication."

Most of this also applies to GPUs, which are currently used for AI (which in its current form is sometimes derogatorily called "just linear algebra").

2) The cited blog post doesn't provide enough evidence either for the claim that "This finding underscores the feasibility of leveraging FPGAs to accelerate quantum computing simulations":

The time complexity argument looks suspicious, because getting an exponential speedup in a classical computer would imply that real(not simulated) quantum computers wouldn't be needed anymore. It probably requires an exponential amount of chip area in the FPGA instead, which wouldn't scale much beyond the 5-qubits tested.

3) A large portion of the section comes from a single IP and cites a single blog post, which looks a lot like self promotion. I respect personal projects that come from a "hackers spirit"(technological curiosity), but presented as a research finding, this is not scientific enough for a Wikipedia article. 84.141.144.13 (talk) 16:14, 26 May 2024 (UTC)