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Because we're in beta and have little established history of on-topic-ness, it's likely that quantum computing enthusiasts will come here and ask questions that would be appropriate, or even more appropriate, on other sites.

In order to help guide the formation of this site's scope, let us ask "What questions have come up on this site that could have been posted on other sites?"

Each answer here should link to one or more questions and explain why they should be on another site.

For each answer here, vote up if you agree that the linked question should be on another site.

(If a mod can make the answers community wiki so that my meta-rep doesn't get totally trashed, that would be nice)

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    $\begingroup$ While there are uses to answering this question in helping define the scope of this site, it's worth mentioning that just because a question is on-topic on another does not make it off-topic here. In particular, people have been VTC-ing as off-topic because "This is a nice question and would be at home on the physics site", which isn't a valid reason according to this post, specifically the paragraphs on "Avoid migrating answered questions" and "Don't migrate for the sake of migration" $\endgroup$ – Mithrandir24601 Mar 17 '18 at 11:49
  • $\begingroup$ I have to close this thread as an inadvisable activity. Please see my answer for more information — quantumcomputing.meta.stackexchange.com/a/74/3 $\endgroup$ – Robert Cartaino Mar 17 '18 at 19:30
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I have to close this catch-all question review thread as a highly inadvisable activity.

First, if a particular question (or a larger subject space) becomes troublesome in actual practice, the merits of that topic should be raised and discussed in its own thread. Questions can and do get closed by those with that ability/reputation, but to make any question linked here subject to an ongoing pseudo meta poll ("vote up if you agree … this should be on another site") is not how this site is supposed to work.

Regarding the issue of whether cross-site questions should be moved elsewhere, please read

Respect the community – your own, and others’

Folks join this site because they have an interest in "quantum computing". You should uphold that as your scope comprehensively. A question that might also fit elsewhere does not make it off topic for this site. Please be careful about slicing this site up into a patchwork of topics trying to avoid pieces that might also fit on another site.

Unless a question or topic space has been deemed off topic on this site explicitly, we have no cause to remove someone's content for another site, along with the reputation and ownership that goes with it.


A quick note about moving questions to other sites —

Migrations have largely fallen out of favor as a means of moving new questions just asked. Migrations were intended to be used where there was significant content (answers) to be moved to another site when the scope of a site changes. But migrations have too many side effects to use them to routinely move new questions. They tend to make a mess of things (e.g. orphaned content becomes anonymous, improper tags, out of place comments, mismatched voting, ignoring any community guidelines, automatic dupe checks are skipped, etc), so migrations should not be used simply to move a question asked on the wrong site. When there is little content to save, the author should simply flag or delete the question, and re-ask their question in the context of the correct site.

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    $\begingroup$ I am kind of dissapointed by the tone of this post, which characterizes a reasonable and good faith effort to try to understand the scope of this site a lack of respect, and seems to assume that I'm an idiot with no experience contributing on Stack Exchange. The Physics site has gone through a lot of arguing and pain because of unclear scope and I was trying to help avoid that. $\endgroup$ – DanielSank Mar 17 '18 at 20:15
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    $\begingroup$ @DanielSank There was nothing expressed nor implied that this was not well-meaning or done in folly. Nobody is expected to know everything we've learned in building these sites and all the nuances of what can go wrong with certain activities. That's why there's a broad base of community-lead moderation and community managers to help users through this process and to provide this type of guidance when we see a problem re-emerging on occasion. Note that the blog post I cited wasn't even written until four years after we started building sites. Some of these lessons were hard-earned ourselves $\endgroup$ – Robert Cartaino Mar 17 '18 at 20:36
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    $\begingroup$ Note also that not everything I write or comment on is meant for that one person only. I am also talking over their shoulder to the rest of the community... for the enrichment, experience, and (hopefully) future mentoring of others about how/why this stuff works. $\endgroup$ – Robert Cartaino Mar 17 '18 at 20:41
  • $\begingroup$ The OP doesn't mention migration. It doesn't attempt to jerrymander this site. It asks a question meant to encourage a discussion. I posted an answer pointing out how a certain question might look, at the surface, like it should be migrated, and gave an argument that it should not. Taking this opportunity for discussion and construing it as an attempt to strong-arm the site's scope is unfortunate. I cannot give a full discussion of what I'd like to convey in a comment, so I'll ask that you look here. $\endgroup$ – DanielSank Mar 18 '18 at 20:08
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    $\begingroup$ @DanielSank While I do like that you're talking about reptiles, I think you should reread this part of Robert's advice: "But to make any question linked here subject to a pseudo meta poll ("vote up if you agree … this should be on another site") is not how this site is supposed to work. To the unsuspecting user, this activity will only make this community a minefield to navigate." $\endgroup$ – Discrete lizard Mar 19 '18 at 17:30
  • $\begingroup$ @DanielSank I think that while well-intention-ed, this current thread this is a bad idea for two reasons 1) This is indeed confusing for newcomers 2) Whether a particular question should be on or off-topic should be in a separate meta thread, because 2a) this makes it possible to differentiate votes on the importance of the issue and the resolution (off or on topic) 2b) alternative approaches can make posts, instead of comments and 2c) this allows the community to decide to 'feature' individual issues, not a whole bag of issues of which nobody knows when it updates. $\endgroup$ – Discrete lizard Mar 19 '18 at 17:33
  • $\begingroup$ @DanielSank So, basically, your idea is good, but the format is ill chosen. I think its best to trust Robert on the latter, he has a lot experience with this. $\endgroup$ – Discrete lizard Mar 19 '18 at 17:35
  • $\begingroup$ @Discretelizard I'll give my usual response: if you can fix a post by changing a small part of it, do that instead of closing it. $\endgroup$ – DanielSank Mar 19 '18 at 18:07
  • $\begingroup$ @DanielSank Does my point 2 not make it clear that 'fixing the post by changing a small part of it' is impossible? I explicitely mention this current thread is completely ineffective. How can this possibly fixed by even rewriting the entire post in an edit? I'm afraid you should read my comment more careful before giving a canned response! $\endgroup$ – Discrete lizard Mar 19 '18 at 18:15
  • $\begingroup$ @DanielSank Hence, I completely agree with the decision to close. This is a thread that while made with the best intentions, simply should not be. $\endgroup$ – Discrete lizard Mar 19 '18 at 18:17
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If all quantum gates must be unitary, what about measurement?

At a glance, it looks this question could have been on Physics because a good answer probably involves some discussion of physically why measurement is not unitary. I think this question actually does belong on Quantum Computing though, because OP was probably trying to understand the distinction between measurement and gates in their roles in quantum algorithms.

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How does bra-ket notation work?

This is an interesting question because while it's mostly a math question, and would probably be answered by a physicist, it's very relevant to anyone beginning in quantum computation. The Physics site has had to deal with lots of such questions asking about various math notation and concepts necessary to understand physics. It's not clear to me that the Physics site really has a coherent policy on questions like that, and it's not clear that a useful and clear policy can exist.

Might be worth a discussion though.

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  • $\begingroup$ This seems like 'half-meta', in the sense of 'how do I read answers on this site'. Perhaps better to link off-site to Math or Physics in some meta faq. $\endgroup$ – Discrete lizard Mar 21 '18 at 14:20
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What cryogenic systems are suitable for superconducting qubits?

Why do optical quantum computers not have to be kept near absolute zero while superconducting quantum computers do?

Good answers to these questions must talk about the physical realization of qubits and how they respond to their thermal environment. It's wonderful that a person interested in quantum computation wants to know about the physical/engineering aspects of quantum computation, and I think such physics-y questions should be allowed here. However, this question could have been asked on the Physics site.

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    $\begingroup$ I think the community members have already (implicity) agreed that questions related to the making and architecture of quantum computers and qubits is on-topic even though it might also be on-topic on Physics SE. When the site goes public, it would be a good move by the Physics SE community to divert all such questions to this site (you know, to keep them all under the same roof). $\endgroup$ – Sanchayan Dutta Mar 17 '18 at 6:54
  • $\begingroup$ @Blue What's the point of mandating that questions about the physics of a quantum computer come here? I'm sure many physicist users frequent the physics site and are therefore more likely to see and answer such questions if they show up on there. $\endgroup$ – DanielSank Mar 17 '18 at 6:58
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    $\begingroup$ I mean it is okay for a question to be on-topic on both sites. That can't be avoided with the number of sites SE has come up with. But for example since when Code Review SE all the code review type questions started to be sent to the new site. However, after Software Engineering SE came up, not all software engineering questions from SO were diverted there. That created major overlaps between the two sites. I'm not sure if that's something we want. But perhaps we should just let the askers decide which site they want to go with...since overlap is inevitable. $\endgroup$ – Sanchayan Dutta Mar 17 '18 at 7:03
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    $\begingroup$ Relevant: meta.stackexchange.com/questions/129598/… $\endgroup$ – Sanchayan Dutta Mar 17 '18 at 7:06

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