Quantum harmonic oscillator tunneling puzzle

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Discussion Overview

The discussion revolves around the tunneling probabilities of a quantum harmonic oscillator, particularly focusing on the behavior of these probabilities as the quantum number n increases. Participants explore the mathematical implications and interpretations of tunneling in quantum mechanics, comparing classical and quantum behaviors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents a puzzle regarding the tunneling probabilities of a quantum harmonic oscillator, noting that while the probabilities decrease with increasing n, the rate of decrease slows down, leading to questions about the implications of this behavior.
  • Another participant suggests that the observed behavior is a result of mathematical properties inherent to the quantum mechanical framework, cautioning against unsubstantiated claims in textbooks.
  • A participant introduces a comparison to diatomic oxygen's vibrational zero point energy, arguing that achieving classical behavior requires an extremely high quantum number, far beyond the range discussed.
  • One participant claims to have derived an analytical expression for the tunneling probability in the limit of large n, suggesting it matches the observed data.
  • Another participant expresses interest in the theoretical derivation behind the analytical result, indicating a desire for further detail on the calculations involved.
  • Discussion includes a reference to the asymptotic behavior of the quantum wave function and its implications for tunneling probabilities, with some participants expressing surprise at the slow fall-off with n despite the exponential decay in the forbidden region.
  • Several participants engage in technical discussions about the normalization of wave functions and the validity of certain approximations used in their calculations.
  • One participant shares an update about a new animation exploring the Wigner quasiprobability distribution, noting that the interpretation of classically forbidden tails is less clear in this context.

Areas of Agreement / Disagreement

Participants express a range of views on the behavior of tunneling probabilities, with some agreeing on the mathematical results while others question the interpretations and implications. There is no consensus on the exact nature of the tunneling probabilities or the implications of the findings.

Contextual Notes

Participants note limitations in the existing literature regarding the estimates of quantum numbers required for specific tunneling probabilities, highlighting the complexity of the calculations involved and the potential for misinterpretation of results.

  • #31
Avodyne: Please check the new file .
The paper is at the final stages. there is still an "anonymous helper" in the acknowledgments.
 
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  • #33
So would I be right in thinking that this is no longer a puzzle but just a slight surprise? :biggrin:

Actually I found the result a little surprising myself. I think it was because the probability density is a function of both x and n. I naturally expected an exponential dependence on x and I guess this spilled over to expecting a steep dependence on n as well. But as soon as I realized this, I started wondering whether there was any intuitive reason to expect it to fall off with n at all - it would not, AFAIK, go against any fundamental principle if the probability of finding a system outside of its classical range asymptotically approached some constant.
 
  • #34
The old problem of large quantum numbers and the correspondence principle is still being discussed. Cabrera and Kiwi, Large quantum-number states and the correspondence principle, Phys. Rev. A 36, 2995(R) September 1987 show how it can be violated for the harmonic oscillator.
 

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