Talk:Quantum state

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[edit] too technical

The page is nice but it's a bit too technical for non-physics (like me!). Can it be rewritten with more user-friendliness, without perhaps sacrificing completeness?

It would really be nice to see some more on what quantumphysical characteristics of particles define their quantum states.

Technical point: The description of the quantum state as formal and non-physical, as against 'real' measurements, is highly debatable. In many accounts of quantum measurement the quantum state (density matrix) is the _only_ physical reality, the results of a measurement also being expressed in terms of a quantum state. Since everything in the Universe is quantum, including the measuring devices, the idea that the result of a measurement is somehow more 'real' can only be a shorthand for the particular type of quantum state which is produced by interactions with a measuring device and the environment.

The page as it stands gives only an old-fashioned Copenhagen-like account of measurement, which by itself is incomplete and unsatisfactory since it doesn't describe what constitutes a measurement and how the system interacts with what's measuring it.

[edit] Huh?!

I dont know a quark about this theme, but I will like to. I think that after this sentence: "A quantum state is any possible state in which a quantum mechanical system can be.", should come a brief explanation about of those possible states or at least some examples. And then the rest: "A fully specified quantum state can be described by a state vector, a wavefunction, or a complete set of quantum numbers for a specific system."

I agree about the first sentence mentioned above: the opening sentence of the article seems tautologous, and it doesn't become clearer until one reaches the Superposition and Pure/Mixed sections.

Seems tautologous? I've seen billiard balls that weren't as circular as that sentence! "In quantum mechanics, a quantum state is any possible state in which a quantum mechanical system can be." Well, that clears it right up. Gee, thanks. And I suppose the science of physics is the branch of science that deals with physics.

I agree that this article is unclear. It certainly didn't give me the information I was looking for. Fresheneesz 02:28, 22 May 2006 (UTC)

This article is the most impenetrable I've ever seen on Wikipedia, and that's saying something.

The tautology in the opening sentence here is unfortunate, but mostly unavoidable. If any Wikipedian can come up with a precise, friendly definition of a quantum state, then I'd give them a hearty slap on the back, because the fact is that no such definition exists. Quantum mechanics is somewhat self-referential in that respect. A state is how something is. Two states are the same if there is no way to tell them apart via a measurement. That's about the sum of it. Between this and the fuzziness of the definition of 'measurement', you'll find that circular logic is just about unavoidable when dealing with the fundamentals of QM.

[edit] Antimatter

Could someone who knows enough about it please add something about the quantum state necessary for antimatter and matter to annihilate with each other when they come into contact with one another? Thanks!

scienceman 23:18, 23 March 2006 (UTC)

[edit] Merge with excited state, and Energy level

I think it would be a good idea to merge Energy level and excited state with this page. They are all very related concepts, and excited state in particular is a trivial subset of the quantum states - and could easily be a simple section on this page. Any comments? Fresheneesz 02:35, 22 May 2006 (UTC)

I might support making stationary state, energy level, excited state and ground state into the same article. (I think if you want to suggest any of those mergers, then you have to do all of them). On the other hand, I think it's too much to merge it into this article (quantum state). Rather, this article should have a section on stationary states, with a {{main|stationary state}} tag linking to the big article about eigenstates of the hamiltonian (strictly speaking, I think an energy level is an eigenvalue, not an eigenstate, so it's not a quantum state, right? so the proper article to link to is stationary state, not energy level). -lethe ^{talk +} 02:45, 22 May 2006 (UTC)

Sounds like a good plan. I don't know when i'd get to doing that tho. I'll try to start a merge of some of those soon. Fresheneesz 06:00, 22 May 2006 (UTC)

Looking at the articles, I've come to the opinion that energy level should not be merged. There is simply too much to say about calculation of energy levels. So I guess I'm left considering a merger of stationary state, excited state, and ground state. -lethe ^{talk +} 15:50, 22 May 2006 (UTC)

I merged ground level and stationary state, but I don't think theres a good way of merging excited state as well - unles its merged here (quantum state). I don't see a problem with merging those here, its not that much info. And, they all fall under the category of quantum states. Fresheneesz 02:27, 23 May 2006 (UTC)

Please DO NOT merge energy level with quantum state. A quantum state is a distinct entitity, with a number of observables, only one of which is it's (eigen) energy. The energy level entry needs improvement, and should state something like the following: "Multiple states may have the same value of the energy, in which case they are called degenerate states." For example, there are four distinct n=2 states in hydrogen (one 2s, three 2p). In the absence of any external field, they are precisely degenerate. They form an energy level. However, they are quite clearly not the same quantum state, as they result in different values for other observables, such as the electron's angular momentum, or it's projection. Thus, and energy level can contain many quantum states and it is not appropriate to merge this topic with the quantum state topic. I propose we remove the suggestion to merge the energy level article with this one. Az7997 19:08, 2 June 2006 (UTC)

oppose merger quantum state is a specific universe of physics theory. excited states exist in classical mechanics and thermosdynamics. a merger would be nonsense Anlace 03:07, 18 September 2006 (UTC)

[edit] Keep'em seperate

I'm not a total science person, but I know enough to know that they should probably be kept seperate. I think the beauty of wikipedia is to have as much detail as possible on different pages. As long as the topics are well-linked, the info is accessable.

65.211.131.10 21:24, 9 June 2006 (UTC)

oppose merger quantum state is a specific universe of physics theory. excited states exist in classical mechanics and thermosdynamics. a merger would be nonsense Anlace 03:06, 18 September 2006 (UTC)

[edit] Background info added

I added a link to NASA to the excited state page to help make the information a little more user-friendly. That might also be a good base reference for anyone who wanted to make the wikipage more basic/complete.