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 Jan 20 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. $\endgroup$ – Mark S Jan 20 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 Jan 21 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! $\endgroup$ – Mark S Jan 21 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 Jan 21 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!) $\endgroup$ – Norbert Schuch Jan 23 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? $\endgroup$ – Norbert Schuch Jan 23 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 Jan 23 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. $\endgroup$ – Norbert Schuch Jan 23 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 Jan 26 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. $\endgroup$ – Rajiv Krishnakumar Mar 8 at 9:25

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.


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