Talk:Macroscopic quantum phenomena

Observation about quality of article
This article should summarise what Macroscopic quantum phenomena is, in reasonably accessible terms, before it launches into the gobbledegook. — Preceding unsigned comment added by 90.198.198.168 (talk) 12:49, 22 April 2012
 * I modified the introduction. Is it better now?(Adwaele (talk) 07:35, 15 June 2012 (UTC))

I think the article should focus more on how these quantum phenomena become observable at the macroscopic level, and explain these phenomena in language as opposed to mathematical formulae. I am sure the math is quite interesting for physicists. But then again, if you are a physicist looking for info on macroscopic quantum phenomena, Wikipedia might not be the first place you'd check, anyway. 2003:46:8D23:AF01:210:C6FF:FE1F:4ED1 (talk) 19:17, 9 July 2014 (UTC)


 * Agreed. There needs to be less technical, in-words "body" of the article. But the math can stay, underneath the fold... 89.217.26.56 (talk) 16:13, 12 April 2015 (UTC)

Wrong equation or inadequate particle description
From the article:

In quantum mechanics the particle probability flow density J''p (unit: particles per second per m²) can be derived from the Schroedinger equation to be
 * {| width=500px

with q'' the charge of the particle and $$\vec{A}$$ the vector potential.
 * $$\vec{J}_p = \frac{1}{2m}\left(\Psi (i \frac{h}{2\pi}\vec{\nabla} -q \vec{A})\Psi^* +cc \right)$$
 * style="text-align:right"|(16)
 * }

1) Why do we suddenly have a charged particle? This was never said till now. Can the unknown in quantum mechanics spontaneously change from a scalar to a spinor during a derivation?

2) Does this really come from the Schroedinger equation? A plays no role there. And I find a rather different expression for probability flux at Schroedinger equation. Or does it come from the Pauli equation?

3) What is cc?

The section Consequences of the macroscopic occupation in which this equation occurs is, indeed, too technical for what it accomplishes in getting across. Wouldn't it be easier to drop the references to charge and just derive a macroscopic flux for the plain-vanilla Schroedinger equation?

89.217.26.56 (talk) 16:05, 12 April 2015 (UTC)

Scope of article
This article seems to focus on fairly arcane quantum phenomena.

Would it be out of place to expect some mention of more mundane things? If I remember right from my college electricity and magnetism class, most properties of materials aside from their mass cannot be understood classically. For example, classically we'd expect electrons orbiting the nucleus to emit electromagnetic waves and fall into the nucleus. All chemistry is ultimately explained in terms of quantum physics. Also, they tell me that ferromagnetism is essentially a quantum phenomenon, and the basic behavior of transistors is explained in terms of quantum mechanics. — Preceding unsigned comment added by 209.159.232.121 (talk) 18:11, 9 March 2016 (UTC)

Diagram text
This doesn't make much sense. Figure 1 is on the left not the right, also the text for the right says small number, which doesn't seem to match the image. Sun Creator(talk) 11:46, 7 November 2019 (UTC)
 * "Fig.1 right: only one particle; usually the small box is empty. However, there is a certain chance that the particle is in the box. This chance is given by Eq.(3). Middle: a few particles. There are usually some particles in the box. We can define an average, but the actual number of particles in the box has large fluctuations around this average. Right: small number of particles of particles. The fluctuations around the average are small."

Introduction and giant magnetoresistance
One of the introductory sentences at present reads: "The best-known examples of macroscopic quantum phenomena are superfluidity and superconductivity; other examples include the quantum Hall effect, giant magnetoresistance and topological order." Key aspect of "Macroscopic quantum phenomena" is a quantum-mechanical wave function with macroscopic extent. This is definitely given for superfluidity, superconductivity, and quantum Hall effect; "topological order" is a somewhat vague term in this context (but includes quantum Hall effect); but "giant magnetoresistance" is an effect that does not involve any macroscopic wave function, and thus I suggest removing it from the article "Macroscopic quantum phenomena". --MScheffler (talk) 10:18, 23 June 2021 (UTC)
 * Now implemented: "giant magnetoresistance" removed.--MScheffler (talk) 11:57, 20 October 2021 (UTC)