Talk:Quantum computing

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	Quantum computing is a former featured article. Please see the links under Article milestones below for its original nomination page (for older articles, check the nomination archive) and why it was removed.
Article milestones Date Process Result January 19, 2004 Refreshing brilliant prose Kept May 9, 2006 Featured article review Kept May 13, 2007 Featured article review Demoted
Current status: Former featured article

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Material from Quantum computing was split out into List of proposed quantum registers from this version. The former page's history now serves to provide attribution for that content in the latter page, and it must not be deleted so long as the latter page exists. Please leave this template in place to link the article histories and preserve this attribution.

The Wikimedia Foundation's Terms of Use require that editors disclose their "employer, client, and affiliation" with respect to any paid contribution; see WP:PAID. For advice about reviewing paid contributions, see WP:COIRESPONSE. Inkian Jason (talk · contribs) has been paid by Beutler Ink on behalf of Intel via Interfuse Communications.

One sentence reads as follows:

"A classical bit, by definition, exists in either of two physical states, which can be denoted 0 and 1."

This is misuse of the word "physical".

A bit is a concept, not a physical entity. 2601:204:F181:9410:2191:ADEC:5EE:A9CD (talk) 21:30, 23 February 2025 (UTC)[reply]

The light switch in my room disagrees. Johnjbarton (talk) 23:50, 16 April 2025 (UTC)[reply]

I would agree with "physical two states" is incorrect. In a CPU a bit isn't physical, the physical level are transistor based circuits of gates, and the difference between a digital bit ZERO / ONE is a matter of a potential difference of around 1.5 volts DC. The physical level are the (tiny) transistors. EditorÆ (talk) 11:23, 23 July 2025 (UTC)[reply]

The potential difference you are talking about is precisely the two physically distinguishable states of bits inside of a CPU. Information is physical. Electronblues (talk) 07:03, 16 February 2026 (UTC)[reply]

Hello ! I'm impressed by your own page. This is a question, not a statement for you. But there has to be a physical level for everyting existing, doesn't it ? I've read analoguge and digigital theory at university level, but not longer than 6 or 8 weeks.I believed a transistor, gate or CPU etc are physical in the sence they are possible to "touch" ? But a DC potiential difference (mainly defiinating the digital "zeroes" or "ones") cannot be stored or hold in a human hand.

But I may very well be totally wrong in regarding what a Qbit actually is. But I'm under the impression that many "physical Qubits" are requiered in order to create a logical Qubit. (The Quantum Computer wasn't "around" at at all during my edjucation 2000-2003). I'm 61 and am just following the development of the Quantum Computer.

Kind regards EditorÆ (talk) 13:33, 16 February 2026 (UTC)[reply]

Thank you! It is certainly a subtle topic because there are several layers of abstraction involved.

About transistors and DC potential difference-- Imagine a transistor. The transistor is a physical object. But it also has two physical states, high voltage or low voltage. Those two states are physically distinguishable. they correspond to measurably different configurations of electric charges. It's a bit like the weather. We can all tell if it's cold or hot, and we can measure it too, but we can't 'hold' temperature. Nonetheless, it is a physical property because it corresponds to microscopic motion of particles. If you are further interested I recommend reading the article I linked, "Information is physical", by Rolf Landauer at IBM.

The quantum computing topic you are talking about, where multiple "physical qubits" are required to create one "logical qubit" comes from error correction codes in quantum computing, particularly the surface code. In this case, the two physical states of the 'logical qubit' are global properties of the entire lattice formed by the physical qubits. But I want to stress that this, again, is two physical states corresponding to different configurations of the lattice. They are just not the same two physical states as the two physical states of the physical qubits.

The initial sentence is a bit confusing because 'bits' in mathematics or information theory are abstract concepts. But in order to do computing, bits are always implemented physically, and thus always "exist in either of two physical states". This is why the sentence in this context is technically correct, although confusing. Electronblues (talk) 22:38, 16 February 2026 (UTC)[reply]

Well "bit" starts out as a word in the English language and then it needs to get defined. The most technical definitions (i.e. information theory) are a concept rather than a physical device. So I think that 2601 is technically correct. And saying "by definition" IMO makes it more clearly wrong. But by other common meanings/usage it often refers to the physical state, or physical state of a device, or to a device which stores that amount of information. But probably best to tweak the wording a bit, particularly because it claims to be by definition. Sincerely, North8000 (talk) 22:25, 16 February 2026 (UTC)[reply]

All you need to do is create a Class which has an up spin flag and a down spin flag and manipulate that on a classical computer framework. Since we have computers with more than 12 gigabytes of RAM now, it should be possible to simply classically model quantum computation on a (for example) 12 core 12 gigs computer. I don't see how a 100 million dollar 1000 qubit computer is ever going to pay for itself in real-world useful computation. Wade Smith0078 (talk) 16:16, 21 August 2025 (UTC)[reply]

12 GB is nowhere near enough. This is a case of exponential growth. At 50 qubits you're already into terabytes of storage needed. 1000 qubits is well beyond what a classical computer is capable of. MrOllie (talk) 16:30, 21 August 2025 (UTC)[reply]

50 qubits requires petabytes, and the latency issues on such an enormous system would be a significant limiting factor. Tito Omburo (talk) 20:54, 21 August 2025 (UTC)[reply]

Citing or discussing sources is essential in Talk pages since they are not forums. Johnjbarton (talk) 16:43, 21 August 2025 (UTC)[reply]

The dimension of the Hilbert space you need to simulate is 2 n {\displaystyle 2^{n}} where n is the number of qbits. When your computer can store 2 100 {\displaystyle 2^{100}} floating point numbers on the CPU, it might be interesting. This is about 9444732965739290427392 gigabytes. A 1000-bit quantum computer, if simulated on a classical computer, would instantly form a supermassive black hole which would eventually swallow the entire universe (and instantly destroy the solar system). The amount of entropy reuired for such a classical system far exceeds the total gravitational entropy of the observable universe. Tito Omburo (talk) 20:36, 21 August 2025 (UTC)[reply]

The article does not in many cases make a distinction between speculative and theoretical speed-ups, and actual concrete real-world speed-ups over classical algorithms. Yes, Grover's algorithm theoretically gives a speed-up over classical algorithms for NP-complete problems, but there are several reasons to believe that Grover's algorithm will not be able to realize these speed-ups in practice. For one, the speed-ups are over theoretical worst-case complexities, and none of the classical algorithms run anywhere near the theoretical worst-case, so Grover's improvements over the theoretical worst-case is completely irrelevant. One would really need to see whether Grover-like algorithm could also include methods for classical algorithms that much of the time allow avoiding the theoretical worst-case.

The algorithm would need a thorough clean up, to make a clear distinction between theoretical / idealized improvements and plausible real-world speed-ups. Currently the article could be viewed as being full of hype of possibilities that are likely not ever going to be realized. 87.92.236.77 (talk) 20:07, 29 August 2025 (UTC)[reply]

I think a problem is separating the practical from the theoretical aspects. A lot of press and hype fail completely to differentiate, presenting things like even Schor's algorithm as "eventually" practical. But most of quantum computing research has been (certainly historically) on the theoretical side. That said this is a good edit. Tito Omburo (talk) 22:04, 29 August 2025 (UTC)[reply]

Based on this observation, perhaps we could have a section "Speed-ups" or "Theoretical vs practical speedups" to discuss the issues in one place. Or maybe it's just "Theoretical speedups" starting with "Practical speedups from quantum computing have not been demonstrated but certain kinds of improvements are expected based on theoretical analysis." Johnjbarton (talk) 23:05, 29 August 2025 (UTC)[reply]

Actually delving into the article per se, I don't find any big structural problems. Any problems seem to be localized. I haven't even found anything that overpromises. But of course the idea that some (theoretical) quantum computers can solve some NP problems in polynomial time is something that needs to be weighed against the fact that we basically don't actually know the lattice of complexity classes, even in the classical case. Thus the idea that even a theoretical "quantum computer" would beat a classical computer in certain tasks is based on unproven assumptions (many of which likely true, but still are hypotheses). Grover's algorithm is just the lowest hanging fruit, where (to the best of my understanding), no one actually believes iy offers a true advantage. Tito Omburo (talk) 23:19, 29 August 2025 (UTC)[reply]

1. Numbered list item

• Bulleted list item

Hello, we are two members working together to improve this article as part of a course assignment.

We plan to make the following specific improvements to this page:

1. Expanding Key Sections
   • Adding detailed examples to the "Applications" section, such as cryptography, drug discovery, and optimization problems.
   • Adding updated content on current developments in the field of quantum computing, such as quantum hardware and recent advancements by industry and research groups.
   • Clearly describing key challenges in quantum computing, including error correction, decoherence, and scalability.
2. Improving Accessibility for General Readers
   • Simplifying overly technical sections while maintaining accuracy.
   • Adding intuitive explanations alongside technical descriptions to help beginners understand key concepts.
3. Expanding Content on Future Outlook and Challenges
   • Adding a section focusing on the future of quantum computing, including challenges in developing large-scale fault-tolerant systems.
   • Highlighting current limitations in scaling quantum computers.
   • Including information about ongoing research in this domain.
4. Adding Industry and Commercial Development
   • Adding a section on contributions from major technology companies in quantum computing.
   • Including developments across different quantum platforms, such as superconducting and trapped-ion systems.
   • Describing the role of cloud-based quantum computing in advancing the field.
5. Addressing Ethical and Security Implications
   • Adding a section on the impact of quantum computing on current encryption methods.
   • Highlighting potential security risks and challenges.
   • Including current research efforts in post-quantum cryptography.

We will make incremental edits in small revisions and welcome any feedback or suggestions from other editors. Thank you!

Shivani0601 (talk) 21:19, 29 March 2026 (UTC)[reply]

This is an ambitious program for one's first contribution to Wikipedia. Working in small steps is good, but you may find that you revise your own goals as you build more editing experience. I found this essay a useful guide to understanding how writing about technical subjects here works. It is also good to ask for advice at WikiProject Physics. Stepwise Continuous Dysfunction (talk) 06:12, 30 March 2026 (UTC)[reply]

First I want to encourage your work because this is an important article.

I reverted two of your edits. The first one remove sourced content with no WP:Edit summary. Please always use edit summaries and for sure when deleting sources. If the source is on topic and wp:reliable then it should be discussed in the talk page. In the case of

• Brassard, Gilles; Høyer, Peter; Tapp, Alain (2016). "Quantum Algorithm for the Collision Problem". In Kao, Ming-Yang (ed.). Encyclopedia of Algorithms. New York, New York: Springer. pp. 1662–1664. arXiv:quant-ph/9705002. doi:10.1007/978-1-4939-2864-4_304. ISBN 978-1-4939-2864-4. S2CID 3116149.

The source is fine, but it only verifies that Brassard, Høyer, and Tapp's algorithm is based on Grover's algorithm. It does not verify "Many examples of provable quantum speedups". But since I don't know why you deleted the content I don't know how to evaluate the change.

Unfortunately the second edit overlapped the first one. I encourage you to work in paragraph units to minimize this issue. You should be able reapply these changes from the Revision history. Johnjbarton (talk) 23:25, 2 April 2026 (UTC)[reply]

Oh, and this probably goes without saying, but don't use AI. Stepwise Continuous Dysfunction (talk) 17:28, 8 April 2026 (UTC)[reply]

I will be adding information on the History section on the latest developments within the field of quantum computing. I will also expand the discussion in the Challenges section to address new challenges related to global cybersecurity strategies.

--Filmy100 (talk) 19:42, 1 April 2026 (UTC)Filmy100[reply]