I noticed recently that I had edited a posting of an otherwise informed answer solely to replace "q-bit" with "qubit", but then I note that I don't bother to correct the unhyphenated "qbit" to "qubit" when I see it in other similar questions and answers.

Should we have a preferred policy to encourage use of "qubit" in much the same way that we lightly encourage "quantum advantage" or "quantum computational supremacy" over "quantum supremacy"?

Nonetheless there appears to be less than 100 postings that use qbit, while the vast majority, >4k, use qubit, so it might be a don't care in the grand scheme of things. Most of the high-rep users on this site use "qubit" I believe, so I'll go out on a limb and say that "qubit" is preferred but no one will make a stink about "qbit". Maybe some monstrosities like "Q bit" or "quibit" would trigger an edit.

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    $\begingroup$ "qbit" is definitely a monstruosity on par with "q-bit" and such in my book. I edit it anytime I see it, nor I think I'd be able to force myself not to do it even if I wanted to. I do often wonder where it even comes from though. Is it just people than never saw it spelled and go by the way it's pronounced, or is there actually some place in the internet that uses it? $\endgroup$
    – glS Mod
    Commented Jan 20, 2021 at 22:58
  • $\begingroup$ Apparently in David Mermin's book Quantum Computer Science? See here. David Bacon took issue with Mermin's choice here. We actively and happily and gleefully edit |0> to $\vert 0\rangle$ - that of course is fingernails on the chalkboard - but it happens so often that it's hard to keep up. $\endgroup$ Commented Jan 20, 2021 at 23:38
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    $\begingroup$ ah, I didn't know that, I guess that explains why it crops out every so often then. Still, I think it's quite uncontroversial to say that "qubit" is the widespread spelling, used in the overwhelming majority of papers (...right?). Regarding editing posts though... I don't think there's much we can do about it. Most people using these spellings won't read, nor probably care, about we decide here on meta. The only solution that comes to mind is to set up some bot to correct these types of minor spelling mistakes in posts... but I don't think such bots are well accepted in the SE network $\endgroup$
    – glS Mod
    Commented Jan 21, 2021 at 0:02
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    $\begingroup$ Thanks! All of this is probably fun and silly shibboleth talk that doesn't advance QCSE's implied mission to inform and instruct the public on what is known and unknown about the capabilities and limitations of a quantum computer, but it still amazes that "qubit" had not yet been coined by the time of Shor's prime factorization paper. How much easier it is to think about quantum algorithms once "qubit" is internalized! OK Shor's algorithm is still pretty tough for new learners but imagine learning it, or as for Shor, discovering it, without the word! $\endgroup$ Commented Jan 21, 2021 at 0:11
  • $\begingroup$ agree this is probably not so significant in itself but maybe theres something bigger to pursue here. eg a dictionary of standard QC terminology. it would also be interesting to analyze the origins and nuances of slightly different terminology. re q-bit, or qbit, think they are not terrible. $\endgroup$
    – vzn
    Commented Jan 21, 2021 at 21:51
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    $\begingroup$ @glS I think the more natural question is why most people with certain language background (mostly western languages, I guess) feel uncomfortable when they see a "q" without a "u" right after it. (Includes me!) $\endgroup$ Commented Jan 23, 2021 at 15:40
  • $\begingroup$ @Mark "QCSE's implied mission to inform and instruct the public on what is known and unknown about the capabilities and limitations of a quantum computer" -- Is that the mission of qc.se? $\endgroup$ Commented Jan 23, 2021 at 15:42
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    $\begingroup$ @NorbertSchuch mh, that might indeed be a big reason why many find the "qbit" spelling "ugly". Unsurprisingly, it seems to be due to the latin/greek influences in many (most?) European languages. $\endgroup$
    – glS Mod
    Commented Jan 23, 2021 at 17:49
  • $\begingroup$ @Mark Well, for sure there are SE sites which whose target audience are experts of various levels rather than the interested public. Defining the scope if up to the members of qc.se. There have been meta discussions a while ago, and there were diverging opinions IIRC, but given how young this site is, they are potentially outdated. $\endgroup$ Commented Jan 23, 2021 at 18:51
  • $\begingroup$ in some discussions of quantum communication that "qbit" shows up as the simplest construction that follows the same pattern as "cbit", "ebit" and "cobit" and is actually a very natural choice in that context $\endgroup$
    – forky40
    Commented Jan 26, 2021 at 1:51
  • $\begingroup$ I am mostly used to 'qubit', but I don't think we should force everyone to spell it a specific way. The main reasons are (1) as Mark S mentioned, there are legit references that use 'qbit' (2) as mentioned by NorbertSchuch and gIS, there may be cultural reasons why some prefer 'qubit' to 'qbit' or vice-versa, (3) as forky mentioned, there may be legitimate reasons that 'qbit' follows naturally and (4) it's definitely nice to have words for quantum qubits as mentioned by Mark S but nobody is really confusing the term 'qbit' with anything else, so there's no upside in policing the word. $\endgroup$ Commented Mar 8, 2021 at 9:25

2 Answers 2


Just for the sake of having it written as an answer, I'll sum up what was said in the comments of the question.

I think it's safe to say that most people here strongly prefer the "qubit" spelling over any other. This is also the spelling adopted in the overwhelming majority of scientific writing on the subject, as far as I can tell, albeit with some notable exceptions such as David Mermin’s book Quantum Computer Science. This was also discussed in some blog posts, e.g. here and here.

I've personally always edited the other spellings any time I've noticed them, and I'd encourage other people to do the same. It is indeed often quite an annoying janitorial task, but we can hardly do anything about it, as most people using alternative spellings are unlikely to read meta posts anyway. Individual repeated offenders can be asked to use the correct spelling of course, but there's always going to be new people coming in writing "qbit" etc.


I think "qubit" should be used instead of "qbit", "q-bit", or "Q bit" always, unless one of the other spellings becomes more popular overall (in the whole world, not just here on Stack Exchange, and I don't think one of those spellings will become more popular than "qubit" anyway).

  • If you see "qbit" on a new post, feel free to edit it if you have enough reputation to make edits without having to bother reviewers with such a "trifle" matter.

  • If you see "qbit" on an old post, feel free to edit it on an "isolated basis" if you have enough reputation to make edits without having to bother reviewers with such a "trifle" matter.

  • However, if you're thinking of going through 100 old posts and editing just "qbit" to "qubit", then what you'll be doing is bumping up 100 old posts to the top of the site's list of questions, and this will make the recent questions (often by new users who are just about to get their first experience of whether or not this is a good place to ask a quantum computing question) get buried.

    • Buried questions lack visibility and because of that might never get answered.

    • If people's first impression of the site is that their question doesn't get answers, they are less likely to come back, and that is not exactly what we want here.

So please feel free to edit the spelling if you have enough reputation to make edits unilaterally, as long as it's on new questions or an isolated old question (not on 100 old questions at the same time, for example).

  • $\begingroup$ The last parenthetical can probably be generalized to avoid block-editing a bunch of questions for other similar issues. Richard Jozsa's name is spelled with the "z" first; however about 20% (20 of 94) of all posts that mention Jozsa or Deutsch-Jozsa spell as Josza with "s" first (many posts by me embarrassingly!) Unlike qbit vs. qubit, however, there's just no controversy about whether we should take a stand on spelling his name correctly (we should). $\endgroup$ Commented Apr 16, 2021 at 22:53
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    $\begingroup$ @MarkS Interesting. I hadn't noticed there's been so many misspellings of Jozsa! We should take a stand on it, but I think the right way to do it is to catch it when it first happens, and perhaps do 2-3 edits at a time sporadically to correct the rest of them. It seems that it was spelled josza only 20 times and I've just corrected it on the most recent 3 of these posts (two of these were your posts!). Maybe next week we can do another 3, and at 3/week we'll get them all fixed soon enough :) $\endgroup$ Commented Apr 16, 2021 at 22:59
  • $\begingroup$ I suppose one way to work around the issue of accidentally burying new questions is to edit affected new questions after the bulk edit is complete. It is generally not a problem to find something about a new question to improve (typos, spelling, capitalization, terminology, mathjax, grammar, punctuation, removing unnecessary text like "Thanks!" etc). Is there a reason this should not be done? $\endgroup$ Commented Apr 16, 2021 at 23:25
  • $\begingroup$ @AdamZalcman That's also doable, and a good idea. I think the issue though is that: how do you choose which questions to unbury? There's 17 more posts that use the mis-spelling "Josza", and correcting the spellings would push about 50 questions into lower visibility. Also, even more than 50 questions will be affected in the "active questions" page. I suppose 50 or 50+ questions to unbury, is quite a bit much! $\endgroup$ Commented Apr 16, 2021 at 23:32

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