Symmetric Potentials - Eigenstates & Ground States

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Discussion Overview

The discussion revolves around the properties of eigenstates in symmetric potentials, specifically addressing whether eigenstates must be symmetric or antisymmetric, and the nature of the ground and first excited states in such systems. It touches on theoretical aspects of quantum mechanics.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants propose that if a potential is symmetric, the eigenstates are either symmetric or antisymmetric.
  • One participant asserts that the ground state is always symmetric and the first excited state is always antisymmetric, but this claim is questioned.
  • Another participant suggests that the ground state wave function in one dimension has no zeroes, implying a reason for its symmetry.
  • One participant argues that while a symmetric potential allows for a basis of symmetric and antisymmetric eigenstates, it does not guarantee that all eigenstates must conform to this symmetry.
  • There is a claim that there are no degenerate eigenvalues in one dimension, though this is later qualified with uncertainty regarding its validity in cases such as a constant potential.
  • A participant expresses doubt about the general applicability of the statement regarding degenerate eigenvalues, especially in continuous spectra.

Areas of Agreement / Disagreement

Participants express differing views on the implications of symmetry in potentials and the nature of eigenstates, indicating that multiple competing views remain without consensus.

Contextual Notes

The discussion includes limitations regarding the assumptions about eigenstates and the conditions under which statements about degeneracy hold true, particularly in specific potential scenarios.

MJC3Jh
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Hi,

Can anyone help me to understand the following please? If a potential is symmetric does this mean that the eigenstates are either symmetric or antisymmetric? Is the ground state always symmetric and the first excited state always antisymmetric?

Thanks!
 
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Yes and yes.
 
Why is the second bit true?
 
The ground state wave function in one dimension has no zeroes. You can probably google for a proof.
 
MJC3Jh said:
If a potential is symmetric does this mean that the eigenstates are either symmetric or antisymmetric?
Not necessarily, IMO. You can always choose the basis consisting of symmetric and antisymmetric eigenstates of the Hamiltonian though, as the parity operator commutes with the Hamiltonian. But this is not the same as what you ask, as a symmetric and an asymmetric eigenstates can have the same eigenvalue, so their linear combination will also be an eigenstate.
 
There are no degenerate eigenvalues in one dimension.
 
Avodyne said:
There are no degenerate eigenvalues in one dimension.
I guess this statement should be qualified somehow, because it is clearly doubtful in the case of a constant potential. My guess is the statement does not hold water in a more general case either, at least for the continuous spectrum. If you have infinitely high walls, I don't know, maybe you're right.
 

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