How to derive the energy of a parabolic confining potential in a wire

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Discussion Overview

The discussion revolves around deriving the energy of a parabolic confining potential in a wire, with references to harmonic oscillator models and the incorporation of magnetic vector potentials. Participants explore various approaches and equations related to this topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant seeks guidance on deriving the energy expression for a parabolic confining potential in a wire, referencing a specific equation from a source.
  • Another participant inquires whether the book provides a Hamiltonian for the particles in the wire.
  • A question is raised about how to incorporate a magnetic vector potential into the Hamiltonian.
  • A participant mentions that the book provides a simple harmonic oscillator (SHO) equation in Landau gauge, questioning its applicability in the derivation.
  • One participant suggests using the form for parabolic magnetic confinement provided in the source, indicating that it may eliminate the need for the vector potential.
  • There is a discussion about whether to use a specific form of the potential, V(x) = mw0x^2/2, and how it relates to the equations being referenced.
  • A participant asks if an expression for the wave function u(x) is necessary to solve for the energy of the confining potential.
  • Another participant confirms that the potential can be expressed using a redefined origin and suggests that it resembles a SHO Hamiltonian.

Areas of Agreement / Disagreement

Participants express uncertainty about the appropriate form of the potential and the necessity of incorporating the magnetic vector potential. There is no consensus on the best approach to derive the energy expression.

Contextual Notes

Participants reference specific equations and definitions from a source document, indicating that the derivation may depend on these definitions and the context of the problem. There are unresolved aspects regarding the integration of the magnetic vector potential and the exact form of the potential used in the derivation.

john chen
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Hi all,

How to derive the energy of a parabolic confining potential in a wire as shown below? I tried to follow the derivation of the harmonic, oscillator like we did for the quantum well and the magnetic field but i can't find anything that has an expression that come close to the one shown below.

241911
where
241913


I really have no idea how to start and i really appreciate if anybody is willing to guide me or help me. Thanks...
 

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Did the book explicitly give a hamiltonian for the particles in the wire?
 
Do you know how to incorporate a Magnetic Vector Potential into the Hamiltonian?
 
Hi all, thanks for replying! @stevendaryl The book doesn't really give a hamiltonian for the particles in the wire but its gives a SHO equation in landau gauge which gains confining potential
241940
which I am not sure can it be used in pkace of that?

@hutchphd I have never done anything related to magnetic vector potential into hamiltonian so far so if is really needed, i would like to know how is it done..Anyways the link to the equation for energy of confining parabolic potential can be found in this link http://macbeth.if.usp.br/~gusev/Davies.pdf page 249, equation 6.53
 
john chen said:
@hutchphd I have never done anything related to magnetic vector potential into hamiltonian so far so if is really needed, i would like to know how is it done..
I see that he gives you the form for the parabolic"magnetic" confinement just before 6.53 so you don't really need to go to Vector potential (any quantum text will have it if you are interested). So put that into V(x) in 6.52 and regroup terms using the definitions immediately after 6.53. It should then look like the 2D SHO in directions perpendicular to wire axis. Therefore you can write down the eigenvalues using these new definitions which contain the parameter B to obtain 6.53. The k is along the wire axis
 
Last edited:
@hutchphd @stevendaryl So is V(x) = mw0x^2/2 or the one that is circled in blue below equation 6.52? Because I went to spend a few hours using V(x) = mw0x^2/2 into equation 6.52
241966
but to no avail I can't link it to the definitions
1555344672555-png.png
.
241965
 
And do I have to introduce an expression for wave function u(x) to solve for the energy of confining parabolic potential?
 
john chen said:
1555397422964-png.png
Yes he does redefine the zero point for x as you point out ( I missed that), express the potential using (x-xk ) and consolidate terms.

john chen said:
And do I have to introduce an expression for wave function u(x) to solve for the energy of confining parabolic potential?
You need only to then say "hey, this is exactly a SHO Hamiltonian with a redefined origin for x and a funny mass etc" and write down the known corresponding solution for whatever you need.
 
@hutchphd ah I see, so I do still use V(x) = mw0x^2/2 for equation 6.52? Anyways thanks for helping, really appreciate!
 
  • #10
john chen said:
@hutchphd ah I see, so I do still use V(x) = mw0x^2/2 for equation 6.52? Anyways thanks for helping, really appreciate!
It should be quadratic in (x-xk) and expressed using w0 I think. You can make it work.
 

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