# Is "quantum mechanics" and "quant-ph" the same?

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or else: how refined tagging system would you like to have?

On one hand, it is good to have a precise thematic separation of different topics. On the other hand, if you have lots of tags denoting something similar, people will start using them quite arbitrarily, as for example the practice on Mathoverflow shows.

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retagged Mar 7, 2014
+1: This is a very good observation. Thank you for posting.

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In the early days of the physics site I came up with a [list of subfield tags](http://meta.physics.stackexchange.com/questions/8/physics-subfield-tags-and-general-tag-rules), which may or may not be useful for you.

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Agreed, at some time during the Beta we should start the merging. I suggest however we wait a while and see what type of Tags the community prefers (Public Beta?). I believe the two dilemmas we will be facing are:

Full Title Tags vs. Short Tags

General Tags vs. Localized Tags

Just seems cleaner to have one style of tagging. Personally I prefer Localized Full Title Tags (Like "Quantum Mechanics").

Even though I'm not the biggest fan of the following, we could also consider a mixture "Short Version . Long Version", as found on MO (Example: "ag.algebraic-geometry").

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answered Sep 17, 2011 by (230 points)
For ag.algebraic-geometry, MO just lifted the arXiv tags, which worked very well for mathematics. The arXiv tags didn't work as well for TCS stackexchange. For TP, I don't know what will work well.

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In the context of this site, the bulk of the questions we anticipate will come from research physicists (or atleast graduate students in theoretical and mathematical physics and upwards) -- so I would say the distinction is fairly substantial. ... (A proposed distinction (but still under discussion) is to use an arXiv identifier + plus additional identifiers specific to the exact topic(s) of the question, i.e. as refined as possible given a limit of five tags per post.)

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answered Sep 17, 2011 by (155 points)
It was clear to me that the difference is substantial. However, the question is, how substantial. Will people use it correclty? And, more importantly (but connected), will people find what they are looking for if there is a plethora of tags?

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I think, at bare minimum, there is the mathematical physics vs. theoretical physics division: mathematical "quantum mechanics", with all the attendant issues and topics that mathematical physicists deal with (e.g. operator algebras, spectral analysis, related functional analysis topics, etc.); and "quantum physics" from the theoretical physics perspective (as in the arXiv classification). ... Apart from that, the distinction can be as specific as the poster wants. ... whatever allows the community members to categorise their posts in the most relevant manner.

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This is why the community usage will decide on these matters. At this moment (though too early) I do not see any distinction in usage of the two above mentioned tags.

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I agree. ... I'm requesting members who've posted questions on [Physics SE](http://physics.stackexchange.com) to voluntarily repost (and delete from PSE) questions more appropriate for this site. ...

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I see no distinction whatsoever between to the two. The arXiv defines quant-ph as quantum physics which is clearly synonymous with quantum mechanics. The newer engine incorporates tag-synonyms which will sort out some of the confusion by automatically retagging questions. (I don't know if MO has it being a stackexchange 1.0 site.) The difficulty lies with choosing which one is the main term, i.e. does quantum-mechanics point to quant-ph, or vice verse. Towards that end, I'm a fan of full tags for clarity, but I think generality vs. locality will work itself out.

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answered Sep 19, 2011 by (240 points)
There is a substantial body of mathematical physics relating to mathematical "quantum physics" vs. the sorts of papers you find at "quant-ph" per se. (as for example: J. Glimm / A. Jaffe's [Quantum physics: a functional integral point of view](http://books.google.com/books?id=HxGfqiT8_eAC&q=%22Quantum+Physics%22+Jaffe&dq=%22Quantum+Physics%22+Jaffe&hl=en&ei=d8F2TuCGDsOziQectPixDQ&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CC8Q6AEwAA) ...

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... and B. Simon's [Functional integration and quantum physics](http://books.google.com/books?id=6Wcaa2ddplEC&printsec=frontcover&dq=%22Quantum+Physics%22&hl=en&ei=WcF2TsCIIOrqmAXWupDXDA&sa=X&oi=book_result&ct=result&resnum=8&ved=0CFcQ6AEwBzgU#v=onepage&q&f=false), among others). They are both mathematical physics books, not necessarily "quant-ph" as physicists interpret it.

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@UGPhysics, those are examples of techniques that not everyone would use. But, to say that they are not about quantum physics is to imply that there is a clean separation between math-ph and quant-ph which [doesn't exist](http://arxiv.org/abs/1109.3575). That said, how does this relate to the distinction between quantum-mechanics and quant-ph?

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I've once come across this distinction (I can't recall off the top of my head where: most likely on the Net): "quantum mechanics" is the specific physical theory developed by the pioneers (i.e. during 1920's and early '30's) (it is per se a *physics theory*, similar to Newtonian mechanics developed by Newton); "quantum physics" subsumes 'quantum mechanics' and includes current research areas; plus, according to the community in question - it can refer either to mathematical area(s) which grew out of the theory ...

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... (to refer to abatkai's [profile](http://meta.theoreticalphysics.stackexchange.com/users/123/abatkai) and the works above), or it can mean areas which theoretical physicists tend to study ... the distinction is blurred in many instances, I'll admit: but there is *substantial* separation between what a mathematical physicist would be interested in vs. what a primarily quantum physicist (theoretical physicist) would be interested in. ... You can ask those who are far more expert than me, and judge for yourself.

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@UGPhysics, forgive me, but I still fail to see the point your trying to make and how it relates to the point I was making.

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as per your answer: "quantum physics ... is clearly synonymous with quantum mechanics":- I'm saying this isn't exactly correct: quantum mechanics (is generally meant as) the Heisenberg / Schroedinger, plus by others (e.g. Dirac, et al), theoretical-mathematical framework to provide quantitative answers to direct experiments within the applicable scale of qm; on the other hand, "quantum physics" includes not just the framework, but current research into many areas in the scale-range of qm, e.g. quantum computation, decoherence, etc. -- (as the arXiv category provides a much ...

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... better profile of). ... Meanwhile, mathematical / rigorous investigations on this *framework* tend to fall within the purview of mathematical physics (to illustrate from the above examples); and in some cases ideas developed in the process have little or nothing directly to do with physics, e.g. functional analysis, representation theory, (maybe also operator algebras - I'm not exactly certain of this though) and other purely math topics initially inspired by 'quantum mechanics'. ...

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... The [poster](http://meta.theoreticalphysics.stackexchange.com/users/123/abatkai) is a mathematician working in functional analysis- and wanted to know how much of a distinction we make between the two terms. -- If I've not misread his question, he wants to know if purely math-oriented questions (of the sort math-physicists would make) would be suitable here (as we call the site "Theoretical Physics").

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@UGPhysics, I think you've read into the question somewhat. To me it is a question on the distinction between two very similar things, in addition to a caution about what occurs with such fine distinctions.

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@UGPhysics, as to quantum mechanics v physics, I dimly recall hearing that distinction before, yet everyone I talk to uses mechanics, not physics. Also, "quantum mechanics" has an adjectival form that "quantum physics" does not, and it is in very common usage, e.g. a "quantum mechanical" description of the system. To me, that implies that quantum mechanics is preferred over quantum physics. This may just be the culture at my grad school, but I don't see any meaningful distinction between the two.

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Yes. For most purposes I too don't think it matters much what term is used. But given that we're trying to attract professional mathematical physicists -- (and individuals such as the poster himself) -- I think it should be raised and discussed -- as the poster does, and we're doing... ... Regarding the question of having too fine a distinction, I think the gradual usage of the site will determine the extent of granularity. ... The initial purpose of the site was to serve the theoretical and mathematical physics community the way MO serves the mathematics community. .. So I think the level...

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of granularity should be atleast a degree -- or, more appropriately, two -- of what is used in Physics SE questions on theoretical / mathematics physics.

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@UGPhysics, you have a point that it needs to be discussed, especially to an outsider. However, I don't recall the last time I've heard quantum physics in professional usage. My exposure is limited to the CM community, so it may not be true outside of that. That said, synonyms will provide us with a reasonable defense against the ad hoc usage found in MO.

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True. The two terms seem trivially interchangeable. A tagging guide for first-time users to the site might prove useful.

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