Quantum Harmonic Oscillator Operator Commution

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Discussion Overview

The discussion revolves around the commutation relations of operators in the context of the quantum harmonic oscillator. Participants explore the mathematical derivation of the commutation relation [\widehat{a},\widehat{a}^{+}] and the mistakes made in the calculations. The scope includes mathematical reasoning and conceptual clarification related to quantum mechanics.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • The participant initially claims to have made a basic mistake in calculating the commutation relation [\widehat{a},\widehat{a}^{+}] and ends up with an incorrect result of 2!.
  • Another participant suggests that the original poster should share their calculations to identify the error.
  • One participant mentions the use of bilinearity and anti-symmetry properties of the commutator operation as part of the proof, indicating that the proof appears straightforward to them.
  • The original poster acknowledges a mistake in their approach and expresses a desire to understand where they went wrong.
  • Ultimately, the original poster realizes they incorrectly treated certain expressions as commutators when they should not have been.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial calculations, but there is agreement that the original poster made an error in their reasoning. The discussion reflects a process of clarification rather than a definitive resolution of the mathematical issue.

Contextual Notes

The discussion highlights the importance of correctly applying mathematical operations in quantum mechanics, particularly in the context of operator algebra. Specific steps in the original poster's calculations remain unresolved.

TupoyVolk
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Quantum Harmonic Oscillator Operator Commution (solved)

EDIT
This was solved thanks to CompuChip! The entire post is also not very interesting as it was a basic mistake :P No need to waste time

This is not homework (I am not currently in college :P), but it is a mathematical question I'm stuck and I would greatly appreciate help.

The Quantum harmonic oscillator Operator method uses:

[tex]\widehat{a}[/tex] = [tex]\sqrt{\frac{m\omega}{2\hbar}}[/tex]([tex]\widehat{x}[/tex] + [tex]\frac{i\widehat{p}}{m\omega}[/tex])
and
[tex]\widehat{a}[/tex][tex]^{+}[/tex] = [tex]\sqrt{\frac{m\omega}{2\hbar}}[/tex]([tex]\widehat{x}[/tex] - [tex]\frac{i\widehat{p}}{m\omega}[/tex])

It also says that:
[[tex]\widehat{a}[/tex],[tex]\widehat{a}[/tex][tex]^{+}[/tex]] = 1

[[tex]\widehat{a}[/tex],[tex]\widehat{a}[/tex][tex]^{+}[/tex]] = [tex]\widehat{a}[/tex][tex]\widehat{a}[/tex][tex]^{+}[/tex] - [tex]\widehat{a}[/tex][tex]^{+}[/tex][tex]\widehat{a}[/tex]

I keep ending up with 2!

Here is a "proof"
http://quantummechanics.ucsd.edu/ph130a/130_notes/node169.html
But they have simply multiplied [tex]\widehat{a}[/tex][tex]\widehat{a}[/tex][tex]^{+}[/tex]

I feel like I cannot continue(self-study) until I see how I'm wrong. Please help!
 
Last edited:
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TupoyVolk said:
I keep ending up with 2!
Then you're doing something wrong :P
For us to see what exactly, you could post your calculation (either scanned or - preferably - nicely TeXed)

But they have simply multiplied [tex]\widehat{a}[/tex][tex]\widehat{a}[/tex][tex]^{+}[/tex]

I don't see where they did that. I just see them using the bilinearity of the commutator operation, i.e.
[r x, y] = r [x, y] (when r is a real number and x, y are operators - sorry, don't feel like putting hats and stuff)
[x + y, z] = [x, z] + [y, z] (where x, y, z are operators)
together with anti-symmetry ([x, y] = -[y, x]).

The proof looks really straightforward to me, can you maybe try to explain which step exactly is giving the problem?
 
Thank you so much for the reply.:smile:
I believe I am wrong, because QM indeed works! I just "need" to see how.

What was written where this sentence is, had a very stupid mathematical mistake. :)

I cannot see where I am wrong.
 
Last edited:
Holy crap.
I see my giant fail.

For some reason I turned things into commutators that shouldn't be them.
Thank you so much!
 

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