Doubt in the quantum harmonic oscillator

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Discussion Overview

The discussion revolves around the quantum harmonic oscillator, specifically focusing on the properties of the annihilation and creation operators, the number operator, and the implications of eigenvalue degeneracy in the context of quantum mechanics. Participants explore the conditions under which the eigenstates of the number operator are considered non-degenerate and the physical reasoning behind this assumption.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant references Sakurai's treatment of the harmonic oscillator, questioning the assumption that the spectrum of the number operator ##N## is non-degenerate for the eigenstates ##|n \rangle##.
  • Another participant notes that labeling eigenvalues by energy implies non-degeneracy, suggesting a connection between the eigenvalues and their physical interpretation.
  • A participant seeks clarification on whether the non-degeneracy of the eigenstates is a necessary condition and questions the physical rationale behind this requirement in the context of the harmonic oscillator.
  • One participant suggests consulting introductory textbooks, like Griffiths, for further insights into the topic.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the necessity of non-degeneracy in the spectrum of the number operator and the Hamiltonian. Multiple competing views remain on the implications and physical reasoning behind these assumptions.

Contextual Notes

The discussion highlights potential limitations in understanding the implications of eigenvalue degeneracy, as well as the dependence on definitions and interpretations of quantum mechanical operators.

Lebnm
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I was reviewing the harmonic oscillator with Sakurai. Using the annihilation and the creation operators ##a## and ##a^{\dagger}##, and the number operator ##N = a^{\dagger}a##, with ##N |n \rangle = n | n \rangle##, he showed that ##a | n \rangle## is an eigenstate of ##N## with eigenvalue ##n - 1##, so he concludes that ##a | n \rangle \propto | n - 1 \rangle##. But, to it be true, the spectrum of ##N## should be non-degenerated, shouldn't it? Is this true? Can I proof this?
 
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You already label the eigen values by their energy, which relies on that the eigenvalues are non-degenerate.
 
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So, in the definition of the eigenstates of ##N##, I am imposing that they are non-degenerated, right? Is there some physical reason to do this? I can't see why the spectrum of ##N##, and consequently the spectrum of the hamiltonian, need to be non-degenerated in a harmonic oscillator.
 
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Lebnm said:
I can't see why the spectrum of ##N##, and consequently the spectrum of the hamiltonian, need to be non-degenerated in a harmonic oscillator.
You'll have to look in an introductory textbook, such as Griffiths.
 

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