Talk:Quantum decoherence

Puzzling and incorrect lede

The first sentence says:

• Quantum decoherence is the loss of quantum coherence, the process in which a system's behaviour changes from that which can be explained by quantum mechanics to that which can be explained by classical mechanics.

The sentence makes no sense: does "the process" refer to coherence or decoherence? We can infer the latter, but then the sentence would be disputed. See

• A J Leggett 2002 J. Phys.: Condens. Matter 14 R415 DOI 10.1088/0953-8984/14/15/201

Johnjbarton (talk) 17:16, 4 May 2024 (UTC)

“lost” energy doesn’t exist

The end of the second paragraph in the Concept section says "As a result of this process, quantum behavior is apparently lost, just as energy appears to be lost by friction in classical mechanics." Classical mechanics are governed by laws of thermodynamics, the first of which is energy conservation. Hence, energy doesn't get "lost" by friction. The example should be revised, or if no classical mechanic equivalent exists, removed Jpcarbod (talk) 04:49, 6 July 2024 (UTC)

I revised the sentence but it could be removed as unsourced. Johnjbarton (talk) 15:29, 6 July 2024 (UTC)

Concept

I believe the phrase " a mathematical representation of the state of the system" should be changed to "a mathematical representation of the probable state of the system after measurement".

Though often forgotten, that is just what the Born law tells us. There are many, many authoritative publications to confirm this understanding, starting with Born's original analysis: M. Born. Z. Phys. 37, 863 (1926). One among the many others is Wigner's 1952 article in Z. fur Physik, 133, 101, "Measurement of Quantum Mechanical Operators" where he explains that each of the eigenfunctions of the present wavefunction is a probable result of a measurement, with its accompanying eigenvalue.

I believe this understanding is not at all trivial, since the present wavefunction is often believed to collapse at measurement. D bar x (talk) 21:11, 31 August 2024 (UTC)

The full sentence is:

• "In quantum mechanics, particles such as electrons are described by a wave function, a mathematical representation of the quantum state of a system; a probabilistic interpretation of the wave function is used to explain various quantum effects."

I assume your point is that quantum mechanics makes no predictions other than measurements. I don't think the sentence is really off base. A "state" is an abstraction so its interpretation is not set by the sentence. Johnjbarton (talk) 15:01, 1 September 2024 (UTC)

Zurek's decoherence theory is founded on the assumption that a quantum superposition, as of alive and dead cats, describes the present physical state of the system considered. (See his Physics Today article from 1991.) The state of the system at the present time, meaning, in physics, the physical properties of the system, just as Zurek has interpreted it, and as thermodynamic texts, for example, also interpret it, is NOT what Born's law specifies. Born said the quantum wavefunction predicts the state after the next measurement, not now. That's my point, and why I believe that particular sentence should be improved. D bar x (talk) 21:42, 1 September 2024 (UTC)

The sentence currently in the article could probably be improved, but your suggested revision is, I think, more opaque than what the article currently has. XOR'easter (talk) 19:14, 2 September 2024 (UTC)

Wiki Education assignment: Quantum Information Science and Engineering

This article is currently the subject of a Wiki Education Foundation-supported course assignment, between 19 August 2024 and 6 December 2024. Further details are available on the course page. Student editor(s): Suoyuan Xiao, Phyhuan (article contribs).

— Assignment last updated by Za49 (talk) 03:41, 24 September 2024 (UTC)