Talk:Quantum tunnelling

Concept: uncertainty or wave tail penetration?

The concept section ends with a puzzling discussion of the uncertainty principle and tunneling. I can't make out what it is trying to say.

It was my understanding that the qualitative model of tunneling was continuity of the wavefunction. The wave can't end abruptly at the barrier and thus it tails off with finite amplitude into and through the barrier. That is certainly the implication of TunnelEffektKling1.png later in the article.

I'm sure there is away to say this with the uncertainty principle, but I don't see why that would be advantageous. Johnjbarton (talk) 14:34, 27 August 2023 (UTC)

Agreed, it's very confusing. I intend to rewrite this section, and am currently looking for sources. Wolf's Principles of Electron Tunneling Spectroscopy does introduce tunneling by explicitly referring to the continuity of the probability amplitude (and Born rule) but its not really an introductory text. The approach of J.R. Taylor's Modern physics might be useful. Jähmefyysikko (talk) 18:48, 27 August 2023 (UTC)

The tunneling problem

I'm trying to understand the section "The tunneling problem". It does not seem to be a "problem" but rather an explanation.

It features an animation, which is presumably related to some solution to a tunneling problem. But nothing is said about either.

Both the analytic and WKB one dimensional solutions for tunneling are static, time-independent models. Therefore I assume that the wave packet animation shown here is a linear combination of solutions for different energies combined with a unitary evolution phase factor carefully selected to give a localized envelop. Isn't this original research? If not, what is the reference? Johnjbarton (talk) 00:08, 7 September 2023 (UTC)

The wave packet thing is altogether puzzling. It correctly shows partial transmission of the probability amplitude but, with the time dependent envelop, the partial transmission starts at zero, grows, then decays. What can that mean? What do we expect for the transmission cross section? Zero I suppose. So no tunneling right?

Are we to imagine that the wave packet represents a "particle" advancing from the left? So what then do we make of the transmitted wave? A tiny particle? The mass has split at the barrier? Is that tunneling?

Ok maybe I am beginning to understand why the section is named "the tunneling problem" ;-) Johnjbarton (talk) 00:36, 7 September 2023 (UTC)

And! There are two "quantum" effects in quantum tunneling: 1) transmission at energies below the barrier height and 2) probabilistic quantum transmission. The second is just as important: a full quanta crosses at an unpredictable time. This physical behavior is completely contradicted by the deterministic partial transmission shown by the wave packet animation. Johnjbarton (talk) 02:37, 7 September 2023 (UTC)

No hole?

The intro says

This tunnelling leaves the barrier unaffected (i.e. no hole is created in the barrier)

What can this possibly mean? The potential energy barrier is immaterial: it is a hole! Johnjbarton (talk) 00:17, 7 September 2023 (UTC)

Sheep

The intro has a sentence:

• "It's as though a sheep on one side of a 100m tall wall suddenly appears on the other side without going round."

I get that this analogy might help get the energy barrier concept across. However, it makes quantum tunneling seems "magical", as in defying physical laws. But QM is the physical law and the fact that the wall stops the sheep is the magical part. In quantum tunneling, the barrier is entirely conceptual, an artifact of our model of the system. Envisioning the barrier as a wall leads to ridiculous questions like "is there a hole in the barrier"?

Are the sheep helpful? Johnjbarton (talk) 15:56, 16 May 2024 (UTC)