Talk:Quantum decoherence

mechanism

As a beginner I find this section confusing. It doesn't seem to actually propose a mechanism for decoherence, and the qualitative description afaict is very vague. It makes an analogy with classical thermodynamics, which postulates a mechanism (say if you pour hot water into cold water) where molecules collide with each other, transferring momentum between molecules until after a while, everything has averaged out. But there's not an analogous explanation of how quantum states get entangled.

Also, it talks about a 6N-dimensional phase space and says "the combined state vector time-evolves a path through the "larger volume", whose dimensionality is the sum of the dimensions of the two subspaces" without saying whether this is just the classical analogy, or if it's also supposed to apply to the quantum system. I was going to edit it to say "classical" but I'm unsure enough that I decided to post here instead. In the quantum case, I think the combined system's space is supposed to be the tensor product of the subsystems' spaces rather than the Cartesian product, so its dimension would be m×n rather than m+n. Similarly the phase space's dimensionality is exponential in the number of particles rather than linear. I don't know if that affects the analogy much.

It would be nice if the section could be made a little more clear about these issues. The high dimensionality is required in quantum computing so it shouldn't be allowed to slip out of sight. Thanks! 173.228.123.166 (talk) 10:20, 11 April 2018 (UTC)

Pure state???

How can anyone write an article on decoherence and not define a pure state?????????? — Preceding unsigned comment added by Koitus~nlwiki (talk • contribs) 16:37, 3 November 2020 (UTC)

pedagogical lecture on decoherence and quantum measurement

I'd like to add a reference to a recent arXiv paper relevant to this article. It is a short pedagogical lecture aimed at students of quantum mechanics which explains the modern viewpoint on decoherence and its relation to the measurement problem.

Perhaps a more experienced editor (like @StarryGrandma) can suggest a place to add it to the article, with a description similar to the above or to the abstract below.

https://arxiv.org/abs/2212.02391

Title: Decoherence and Quantum Measurement: The Missing Lecture

Abstract: We give an elementary account of quantum measurement and related topics from the modern perspective of decoherence. The discussion should be comprehensible to students who have completed a basic course in quantum mechanics with exposure to concepts such as Hilbert space, density matrices, and von Neumann projection (``wavefunction collapse''). Zenmach (talk) 21:01, 3 January 2023 (UTC)

@Zenmach, Wikipedia is an encyclopedia, not a place to publicize someone's unpublished lecture. See Wikipedia:What Wikipedia is not, particularly the section on textbooks, which says "The purpose of Wikipedia is to summarize accepted knowledge, not to teach subject matter." StarryGrandma (talk) 22:10, 3 January 2023 (UTC)

Intro section way to long.

The intro tends attract additions in articles but per WP:SO it should be "a concise summary of the article". Johnjbarton (talk) 02:01, 27 February 2024 (UTC)

I made a series of organizational edits so address this issue. Some of the content here deleted as duplicate or too detailed and unreferenced (meaning we can't judge if the detail is important or not). Johnjbarton (talk) 02:32, 27 February 2024 (UTC)