Talk:Quantum state

message: === "which" tag ===
There is a  template in the Spin section, but I think that it can be safely removed. "A quantum system" means "any quantum system", therefore in my eyes it does not make sense to ask which system. Petr Matas 09:09, 8 September 2016 (UTC)
replies: text: This section has additional problems. Relativity is not needed for spin. Not even QM is needed for spin (the classical EM field has spin one). (Also The Pauli equation, usually tossed off as "phenomenological", can be deduced with about the same rigor as the Dirac equation, at least this is the claim in Quantum mechanics, by Walter Greiner.) It is all about under which (projective) representation of  (non-relativistic theory) or under which (projective) representation of  (non-relativistic theory) the solutions of the theory transforms. YohanN7 (talk) 10:38, 10 September 2016 (UTC)
thread_title:  Spin 

message: There is a  template in the Spin section, but I think that it can be safely removed. "A quantum system" means "any quantum system", therefore in my eyes it does not make sense to ask which system. Petr Matas 09:09, 8 September 2016 (UTC)
thread_title:  "which" tag 

message: :This section has additional problems. Relativity is not needed for spin. Not even QM is needed for spin (the classical EM field has spin one). (Also The Pauli equation, usually tossed off as "phenomenological", can be deduced with about the same rigor as the Dirac equation, at least this is the claim in Quantum mechanics, by Walter Greiner.) It is all about under which (projective) representation of  (non-relativistic theory) or under which (projective) representation of  (non-relativistic theory) the solutions of the theory transforms. YohanN7 (talk) 10:38, 10 September 2016 (UTC)
thread_title:  Other problems 

message: I think there is a severe problem with the part of this article between the phrases "A more complicated case is given" and "the particles are arbitrarily far apart."
The problem is with the premise "superposition of joint spin states for two particles with spin 1/2".
In particular, the problem is that a requirement that the two particles be entangled, that is, that they share a single quantum state, is omitted.
The problem can be seen in the case of two particles with spin 1/2 that are not entangled. For any two such particles, this section is incorrect. For example, both particles can be measured with their spins in the down direction. David Spector (talk) 13:18, 14 May 2020 (UTC)
replies: text: The article is perfectly correct. The state in question is the singlet, and it is defined in an equation. The properties that are mentioned are properties of the singlet, not of any quantum state. It wouldn't hurt to mention that this state is entangled, though. Tercer (talk) 15:35, 14 May 2020 (UTC)

text: I went to edit this myself, but then realised that the entire lead is a catastrophe and needs to be rewritten anyway. Tercer (talk) 15:39, 14 May 2020 (UTC)
replies: text: Yes, that bit of the lead is technically correct, but the lead overall is a disorganized, overgrown mess. It's hard to tell how even to start fixing it; quite possibly, the best thing to do would be to ignore it and start an entirely new write-up in a sandbox. XOR'easter (talk) 18:18, 17 May 2020 (UTC)

text: OK, I tried my hand at shortening the introduction. I think it's better than it was before (which is of course not the same thing as being good outright). XOR'easter (talk) 19:38, 17 May 2020 (UTC)
replies: text: Thanks for your work! It did improve, although I concur that it's still not good. It is still too long, and I'm skeptical of putting equations in a lead. Most of the material should me merged into the body of the article. I'll get to it eventually, but I can't make promises as I'm rather busy IRL. Tercer (talk) 21:06, 17 May 2020 (UTC)
replies: text: Yes, I can imagine times when putting an equation in the lead would make sense, but this isn't really one of them — why that vector instead of any of the other equally famous examples? This is a busy time off-wiki for me, too, and not a week/month when I should be starting big new projects here, and planning out a new organization for this article (which might be what's necessary) sounds at least moderately big. XOR'easter (talk) 14:55, 18 May 2020 (UTC)
replies: text: I waded right in here. Please review the new lead, but perhaps reply on the following topic to avoid getting too deep. Johnjbarton (talk) 03:23, 16 June 2023 (UTC)
thread_title:  Error in article? 

message: The current revision has this (unreferenced) sentence in the section on superposition:
The photon state is a superposition of two different states, one corresponding to the photon travel through the left slit, and the other corresponding to travel through the right slit.
As is typical in many cases where "photon" appears, this description misleads readers to imagine tiny balls flying through slits.  "travel" implies time and the interference effect in the double-slit experiment is not based on time.  Or tiny balls.
I will correct this and try to re-point the content towards addressing "quantum state". Johnjbarton (talk) 23:55, 17 June 2023 (UTC)
thread_title:  photon travel