Talk:Quantum algorithm

Merging with the Quantum Algorithm Zoo?
I've been in contact with Stephen Jordan of the Quantum Algorithm Zoo, and he is open to the possibility of merging the very extensive information available there into Wikipedia.

What do you think? — Preceding unsigned comment added by Shai mach (talk • contribs) 00:35, 4 November 2019 (UTC)


 * Typically one adds a section at the *bottom* of the talk page; adding it at the top may cause it to be lost.
 * Regarding the Quantum Algorithm Zoo, it looks like a great resource, yet it looks to me to give much more detail than is appropriate for a Wikipedia article. Sanpitch (talk) 23:56, 5 November 2019 (UTC)

Experimental Quantum Computing to Solve Systems of Linear Equations
Maybe we should add something about this: Experimental Quantum Computing to Solve Systems of Linear Equations

--Vitalij zad (talk) 14:39, 29 August 2013 (UTC)


 * It took six years, yet I just added something on this. 107.0.94.194 (talk) 21:45, 14 February 2019 (UTC)

Quantum / Classical 'equivalence'?
"All problems which can be solved on a quantum computer can be solved on a classical computer."

Although the above may be true in some abstract mathematical sense, I don't think it is true in reality.

David Deutsch describes, in 'The Fabric of Reality' some problems which could be rapidly solved by a quantum computer that could not be solved by any classical computer that could ever conceivably be constructed. (Put another way: classical computers could solve any problem a quantum computer could solve, it the universe didn't impose the constraints that it actually *does* impose.) At the moment, I think the lead into this article might suggest that quantum computers are a bit (or a *lot*) faster than classical computers - but really, it is more than that: quantum computers can actually solve, in the physical universe, problems that will never, ever be solved (in our actual, real universe - as opposed to an abstract, hypothetical one) by a classical computer. 62.232.250.50 (talk) 18:37, 10 January 2014 (UTC)

BQP-complete
Perhaps the article should explain the BQP acronym (I think I can guess, but...) 62.232.250.50 (talk) 19:00, 10 January 2014 (UTC)
 * Yep, just added a description. Jaydavidmartin (talk) 22:58, 7 April 2020 (UTC)

"Exponential speedup"
It is extremely common to use "exponential speedup" very loosely, and say that Shor's algorithm provides an exponential speedup over GNFS. However, given that GNFS already provides sub-exponential factoring (that is, faster than $$c^n$$ for any $$c > 0$$), we should probably change the last sentence in the leading paragraph which claims that Shor's algorithm provides an "exponential speedup". Thoughts?


 * I changed the lede to say "much (almost exponentially) faster" rather than "exponentially faster". Sanpitch (talk) 20:31, 19 March 2019 (UTC)

Quadratically faster than linear?
The introduction says: Grover's algorithm runs quadratically faster than the best possible classical algorithm for the same task, a linear search.

What does that even mean? Surely it doesn't want to imply Grover's algorithm runs in $$O \left(\frac{1}{N}\right)$$, making it faster the more there is to search in. 62.216.5.216 (talk) 15:28, 21 April 2021 (UTC)

Quanta Magazine article
I just saw this: https://www.quantamagazine.org/quantum-algorithms-conquer-a-new-kind-of-problem-20220711/  Billymac00 (talk) 21:51, 14 July 2022 (UTC)

The use of the adverb "probably"
There are numerous cases of the use of the adverb "probably" in the article that are imprecise, inappropriate, and take away from the professionalism and encyclopediac tone of the article. I'd consider removing them. 205.189.94.9 (talk) 17:37, 25 September 2023 (UTC)


 * there were two uses of "probably" in the article. The 2nd one was unnecessary and I removed it. The remaining one is in the introduction: "[quantum algorithms] might be able to solve some problems faster than classical algorithms because the quantum superposition and quantum entanglement that quantum algorithms exploit probably cannot be efficiently simulated on classical computers". Here I think "probably" is actually justified (though maybe a better formulation can be found). As I read it, it means to express the fact that it's a logical possibility that quantum mechanics can be efficiently simulated on a classical computer. If that were the case, then any efficient quantum algorithm would give rise (with no more than polynomial overhead) to an efficient classical algorithm and no relevant speedup would be expected. I think it is a widely shared assumption or expectation that it is not possible to efficiently simulate quantum mechanics (and it is borne out by decades of attempts to find efficient numerical algorithms). An alternative formulation that makes more explicit the current state of knowledge would be: "some [quantum algorithms] are expected to solve their tasks faster than any classical algorithms can, because the many-body quantum entanglement and interference that quantum algorithms exploit cannot be efficiently simulated on classical computers. While no proof of the impossibility of such a efficient classical simulation exists, it is considered very unlikely that such a simulation is feasible in general." (As reference for this "common belief", one could cite John Watrous: "There are several problems known to be in BQP but not known (and generally not believed) to be in BPP.", see, p13.) --Qcomp (talk) 17:29, 27 September 2023 (UTC)