Case in point: Resource to explain quantum effects in "layman terms"?

This question seems to be about quantum physics (pretty clearly), but I'm not seeing much about "computing" there. Are we allowing physics questions that don't relate to computing?

  • $\begingroup$ He raised a meta question too $\endgroup$
    – Didix
    Mar 14, 2018 at 15:52
  • $\begingroup$ @DIDIx13 that question is about a completely differnet aspect of the question I linked. $\endgroup$
    – user7
    Mar 14, 2018 at 15:53
  • $\begingroup$ I actually upvoted both questions but it seemed to me useful to notice he's point of view. (Am I wrong ? or useless comment ?) $\endgroup$
    – Didix
    Mar 14, 2018 at 15:57
  • $\begingroup$ Consider adding the meta-faq tag to this question. $\endgroup$ Mar 15, 2018 at 9:25

3 Answers 3


Drawing a "line in the sand" this early seems rather unwise.

Yes, there needs to be some method for determining if a question is, or is not, on topic for the site. Every stack has to settle that point. Although that point is often in flux on established sites as well. While in beta, especially early private beta, there will be many questions that seem on topic, which later are found to not fit so well after all. Likewise, some questions that are off topic now will probably turn out to be quite on topic at a latter date.

I think it's going to be better for the site's development if borderline questions are handled individually, maybe even after some discussion in chat or on meta, rather than trying to create a set of rules or drawing lines while site scope is still very much open for discussion.

As to the instant question, it seems uncertain why the OP needed to "explain" things to the layman. It seems that it is purely quantum mechanics, and no quantum computing connection at all. As such, I'd think that question is off topic. However, if the OP was trying to explain QC to and the QM was the sticking point in that process. Then, maybe, it would be on topic after all. Then again, maybe not even then.

As to trying to limit on topic to "questions that are about the effects of QP as they relate to implementations of QC", seems rather limiting, either to topicality or to question content. I can conceive of users working with QC having problems with something and posting a question here. Being used to general SE guidelines, they limit the info in the question to what's needed, without a long backstory, thereby excluding that the problem relates to what they're trying to do in QC. Other users see the question, don't see any mention of QC and close as off topic, even though with the mention of the QC connection it would have been considered on topic.

I think that with a question being posted on QC.SE, I'd be inclined to presume there is a QC connection, until shown otherwise. (The instant question seems to not be connected to QC, and does need to be clarified if there is a QC connection to it.) Your suggestions seems to be that there should be a presumption there is not a QC connection unless stated otherwise.

As a final suggestion, it might be possible for a question that's borderline to be edited such that it becomes obvious that there's a QC connection, and what that is. By preference, such ought to be done by the OP, but other users can attempt edits as well, keeping in mind the normal guidelines for non-OP edits. Thereby some questions might be salvaged as well.

  • 4
    $\begingroup$ "Likewise, some questions that are off topic now will probably turn out to be quite on topic at a latter date." Yeah. This happened on the physics site where experimentally oriented questions were not particularly welcome for a while. It's best to not preemptively kick out would could be useful questions. $\endgroup$
    – DanielSank
    Mar 13, 2018 at 3:52
  • $\begingroup$ Can't we think of giving an explanation of QM with relation to quantum information? Or will that also tend towards being off topic? $\endgroup$
    – ak_nama
    Mar 16, 2018 at 5:22

If they're not about "computing", which is one of the words in our name, then they're off-topic.

I'd allow questions that are about the effects of QP as they relate to implementations of QC, but not otherwise. For example, "How does wave-particle duality affect the capability of transmitting signals inside a quantum computer?" (I made this up right now, it's probably not a great example).

However, something like "What is quantum entanglement?" is off-topic. If you ask about the effects of entanglement as it applies to computers, again it's on-topic, but without the essential "computing" part it's not.

  • $\begingroup$ I agree with your point of view regarding this particular question. BTW, would you consider questions about quantum communication and quantum information on topic here? $\endgroup$ Mar 12, 2018 at 19:01
  • $\begingroup$ @Blue do you have an example? In general, no, but again does it pertain to computing? $\endgroup$
    – user7
    Mar 12, 2018 at 19:02
  • $\begingroup$ A question like: "Why exactly is faster than light communication not possible using entangled qubits?" Or rather "Why can't the quantum teleportation protocol be used for FTL communication?" $\endgroup$ Mar 12, 2018 at 19:05
  • $\begingroup$ @Blue no. Something like "Can FTL communication with qubits be used to speed up computations incredibly", with the answer being "no lol that's not possible here's why" would be. $\endgroup$
    – user7
    Mar 12, 2018 at 19:06
  • $\begingroup$ So then what about a question on how is quantum cryptography different from cryptography used nowadays $\endgroup$ Mar 12, 2018 at 21:36
  • 5
    $\begingroup$ Things like quantum cryptography, I'd argue, are different - this is something that requires quantum operations to work at all. Quantum operations are a form of quantum info. processing, which is essentially quantum computing. In other words, if I can draw a quantum circuit for it, but not a 'classical circuit' (i.e. using classical operations), then it should be allowed on this SE $\endgroup$
    – Mithrandir24601 Mod
    Mar 12, 2018 at 21:39
  • $\begingroup$ Yes, if we stick strictly to quantum computing, I agree with @Mithrandir24601 that quantum cryptography should also be off-topic, that's why I pointed to an already existing (and allowed) question. Of course, we could also be less strict in defining what is off-topic, but then also other quantum information questions (like the one on quantum teleportation, which is put on hold currently) should be allowed. $\endgroup$ Mar 12, 2018 at 21:47
  • 6
    $\begingroup$ @ZoltanZimboras Wait a minute! I'm saying that quantum crypto should be on topic! :P As I can draw it as a quantum circuit, but not a classical one $\endgroup$
    – Mithrandir24601 Mod
    Mar 12, 2018 at 21:50
  • 1
    $\begingroup$ @Mithrandir24601 Ah, OK. I misunderstood you. Although the concrete question is mostly about BB84, where one does only single quit operations and measurements - so there is not too much of a circuit there. Secondly, I don't think we should stick to circuits, since adiabatic quantum computation and quantum algorithms with quantum walks should clearly belong to this site. $\endgroup$ Mar 12, 2018 at 21:55
  • $\begingroup$ I think questions about principles in quantum information theory which are important for quantum computation (like entanglement) are on-topic -- independent of whether the word "computing" is used explicitly and independently of a circuit diagram $\endgroup$
    – M. Stern
    Mar 14, 2018 at 20:14
  • $\begingroup$ @Mithrandir24601 Yes, but be aware that some post-quantum crypto questions may be pure crypto. $\endgroup$ Mar 21, 2018 at 11:44
  • 1
    $\begingroup$ Also, @ZoltanZimboras, quantum 'cryptography' is as much crypto as 'locked briefcases' are crypto, see blog.cr.yp.to/20160516-quantum.html for more on this, in particular the section "Security failures of physical cryptography, part 1: locked-briefcase cryptography" $\endgroup$ Mar 21, 2018 at 11:48
  • $\begingroup$ @Discretelizard, I actually agree with you. $\endgroup$ Mar 21, 2018 at 13:19

As for some practical advice, I think that the following rule of thumb is useful:

When in doubt, think very hard and try to see some way this is related to quantum computing

That is, before you go for the 'close: off-topic', try your hardest to see what the OP means and where in QC the question lies. Always assume that the question is about QC! You should 'prove' this assumption wrong to be sure this is off-topic. If you know how this question is 'on-topic', do share your ideas in the comments.

In general, always assume people have good intentions, this way you will likely get something useful, even if their intentions are actually bad.

Also, be aware that physicists and CS-people may have different ideas on what quantum or computing means. So, it is possible that the fact that the question is off-topic is merely due to a misunderstaning.


You must log in to answer this question.