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Our site has been active for around 9 months now, and I think we have all gotten a fair idea of which type of questions are acceptable for us and which type are not. I feel it's time to pen down the scope of our site, for our help/on-topic page. To get some clues on how that page should ideally be framed, you may have a look at the Physics SE: help/on-topic and Math SE: help/on-topic pages.

New users are often confused about how they should frame their questions and whether their questions would be acceptable for us. For instance, we recently came to the conclusion that pure quantum mechanics questions wouldn't be suitable here - they're a better fit for Physics SE. At the same time, quantum information theory questions are on-topic. Thus, it would be helpful to have a handy link containing a detailed explanation of the acceptable topics, to which all users can easily refer.

So please give your suggestions below, about the points we which we should include in our help/on-topic page. The moderators will try to take into account all your points and suggestions, and write up the page in a couple of weeks.

Edit: @MEE reminded that even the Ask about... and Don't ask about... sections on the Tour page need to be updated. You may give your suggestions regarding that too.

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  • $\begingroup$ Something like How to ask a good question would be useful to include as well. $\endgroup$
    – user820789
    Commented Dec 16, 2018 at 18:17
  • $\begingroup$ @meowzz Indeed! I'll try to include that. $\endgroup$
    – Sanchayan Dutta Mod
    Commented Dec 17, 2018 at 17:47

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To reiterate my point in the other question, I think the scope should be quantum information, mostly including the subfields listed in the wiki page on quantum information science (though I do not completely agree with the classification used there). In other words the following should be on-topic:

  1. Quantum computing and related topics (which includes things such as quantum error correction, quantum complexity theory, etc.). "Quantum computing" here also includes anything related to ways to program a quantum device.
  2. Quantum communication, quantum cryptography, and related topics (such as quantum teleportation and quantum dense coding).
  3. Questions about quantum information that are not included in the above (e.g. conceptual questions about quantum entanglement or quantum entropy that not necessarily directly associated with a given protocol).
  4. Questions about the math used for results that belong to the above categories. Now this is a tricky one, because it would essentially make the whole of linear algebra in the scope of the site. I see two ways for these kinds of questions to be fit for this site:
    1. They are asked in direct relation with a topic belonging to the first three categories listed here (e.g. how do you compute the eigenvalues of this quantum circuit?).
    2. It might give a chance to prove the given result using tools common in quantum information theory (mostly bra-ket notation). An example of this sort of question is this one.

This list is not, nor could possibly be, exhaustive (though please suggest major topics that should be explicitly in it that I might be forgetting at the moment).

The main reason for having "quantum information" as scope is that I do not think it is feasible to draw any kind of meaningful line between what is "quantum computing" and what is, say, "only quantum communication".

But so then, one could argue, why is the site called "quantum computing" and not "quantum information"? Well, I think it's a good question, but it is what it is at this point.

About welcoming any question related to quantum mechanics, I quote myself in this related answer:

I strongly disagree with accepting all questions about quantum mechanics, as these are very much on-topic on physics.SE (I mean, quantum-mechanics is literally the top tag on physics.SE). To accept all questions about QM indiscriminately would just lead to an unnecessary amount of duplication. Strongly related questions spread among multiple sites are a pain, for one, because you lose all the advantages provided by the Linked and Related lists, and it is often harder to track them down.

Even limiting ourselves to quantum information topics, there will still be a significant amount of overlap with physics.SE, as quantum information questions are just as on-topic there as they are here. There will also be overlap with other sites such as cstheory (for questions about complexity), maths (for questions about the math behind results), or stackoverflow (for questions about programming on quantum devices). I don't think this is avoidable, but is also not that bad, as this sort of thing is nowadays pretty common among SE sites.

This said, it is also true that one cannot really define an hard distinction between what is "quantum information science" and what is "only quantum mechanics". Again, this is unavoidable, but hopefully most cases will be clearly on- or off-topic, and the edge cases will be handled case by case.

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  • $\begingroup$ is the "measurement" also part of your list of quantum information? I had questions about it but I wasn't sure which stack exchange would be better ... $\endgroup$
    – More Anonymous
    Commented Jun 21, 2019 at 12:57
  • $\begingroup$ @MoreAnonymous depending on how the question is posed, those questions definitely fit into the "quantum information questions" category. Note that there is also a measurement tag $\endgroup$
    – glS Mod
    Commented Jun 21, 2019 at 21:07
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I read through @MEE and @glS' answers. Both have given some excellent points. I've taken those and added some of my own. I'm making this a community wiki post so that other users can edit this answer and make suggestions for improvement.

help/on-topic

Quantum Computing Stack Exchange is a question and answer site for scientists, engineers, mathematicians, programmers and computing professionals interested in quantum computing and quantum information. Please look around to see if your question has been asked before. It’s also OK to ask and answer your own question.

The general rule is that you can ask all answerable questions about quantum computing or quantum information. But please read through these guidelines to ensure that your question can be answered: You may ask questions about:

  • theoretical and experimental aspects of quantum information science.
  • mathematics relevant to quantum information science.
  • engineering and architecture of practical quantum computers.
  • simulation and programming of quantum computers.
  • resource recommendations related to one or more of the above topics.

What topics can't I ask here?

Please don't ask questions about these topics. They have been deemed to be not a good fit for this site. These are questions:

  • about general quantum mechanics, quantum field theories, quantum gravity or quantum foundations without any application or relevance to quantum computing or quantum information. You may get help at Physics Stack Exchange for pure physics questions. See this meta post for more context.
  • based on personal, unpublished or non-mainstream theories, or theories published in disreputable or predatory journals. See this meta post for more context.
  • about mathematics which do not require any prior knowledge of quantum computing or quantum information theory to be solved. You may get help at Mathematics Stack Exchange or MathOverflow for such questions. Make sure that your question is truly on-topic for the target site.
  • about software development or classical computing which have no relation to quantum computing.
  • asking for career advice.

What should I avoid asking?

There are some types of questions that seem to be on-topic but unfortunately cannot be answered on this site. This includes questions that:

  • are overly broad and demand excessively long answers.
  • cannot be answered objectively i.e. opinion-based.
  • are unclear or do not contain enough information to be answerable. Such questions will be put on hold until you fix them. Questions that are extremely off-topic, overly broad or of very low quality, may be removed at the discretion of the community and the site moderators.

If your question is not specifically on-topic for Quantum Computing Stack Exchange, it may be on-topic for another Stack Exchange site. If no site currently exists that will accept your question, you may commit to or propose a new site at Area 51, the place where new Stack Exchange communities are created.

I was initially deliberating whether to put the link to the Wikipedia page on Quantum information science or not. Finally I decided to go ahead and do it as that page excellently summarizes the range of topics our site is meant to cover. We will take necessary action in case that link gets obsolete in the future but I guess it's not useful to worry about that now. As for the Ask about... and Don't ask about... sections on the Tour page, I'm not yet sure we need any immediate change. But OK, we will see that after the help/on-topic page is done and dusted.

If you want to discuss aspects of this post, please join this chat room.

Update: This version has been copied over to the help/on-topic page. It's more or less final and takes into account most of the suggestions made in the comments and chat. But still feel free to make further edits and suggestions.

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  • $\begingroup$ Reading Worldbuilding's on-topic help page, they have a brief paragraph at the top which, personally, I rather like - should we make a similar paragraph of 'this is who we are for', which I feel makes things clearer than a rather lengthy list of bullet points? On a similar note, having a huge list starts to feel like 'only these are on topic' (and is also uninteresting to read) which is something I'd quite like to avoid if possible $\endgroup$
    – Mithrandir24601 Mod
    Commented Dec 23, 2018 at 22:52
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I want to suggest this wording as a starting point for further discussion and the final text:

help/on-topic

The general rule is that you can ask all answerable questions about quantum computing. But please read through these hints to ensure that your question will be answered:

What topics can I ask about here

Our site is for people interested in the application of quantum physics to information technologies. Therefore ask questions about:

  • developing, building or programming quantum computers
  • everything that has to do with both information science and quantum computers
  • the field of quantum computing or quantum information theory

What topics can't I ask here? Please don't ask about these topics. They have been deemed to be not a good fit for this site. These are

questions ...

  • about general quantum mechanics without any application to quantum computing or quantum information theory. You may get help at Physics.
  • asking us to verify personal unpublished theories (non-mainstream). See this for more information.

What should I avoid asking There are some types of questions that seem to be on-topic but unfortunately cannot be answered on this site.

This includes questions that ...

  • are overly broad and ask the answerer to write an excessively long answer
  • cannot be answered objectively
  • do not contain enough information to be answerable

tour

Ask about ...

  • conceptual or practical issues with quantum computers
  • quantum information theory issues

Don’t ask about ...

  • general quantum mechanics (not related to quantum computing at all)
  • your personal quantum information theories
  • unanswerable questions
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