Momentum space particle in a box

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Discussion Overview

The discussion revolves around the energy eigenvalue problem for a particle in a box, specifically exploring solutions in momentum space rather than through traditional differential equations. Participants are examining the implications of using momentum eigenvectors and the challenges associated with boundary conditions in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes using the momentum representation to solve the particle in a box problem, suggesting a state expressed as a linear combination of momentum eigenstates.
  • Another participant suggests looking for linear combinations of free particle solutions that satisfy the boundary conditions of a perfect box, specifically that the wave function goes to zero at the edges.
  • A different participant mentions a previous attempt to apply a similar approach to the infinite square well, concluding that it was not feasible, and references another thread for context.
  • Another contribution raises concerns about the Fourier transform of the potential, describing it as complex and noting difficulties with boundary conditions in momentum space, as well as the non-hermiticity of the momentum operator which affects eigenvalue considerations.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of using momentum space for this problem, with some suggesting it may be possible under certain conditions, while others highlight significant challenges and limitations. No consensus is reached on the approach or its validity.

Contextual Notes

Participants note limitations related to boundary conditions, the nature of the momentum operator, and the implications of using momentum eigenstates in a bound problem. These factors contribute to the complexity of the discussion.

tomothy
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I am trying to formulate a solution to the particle in a box energy eigenvalue problem, without solving a differential equation, instead using eigenvectors of p^2. My idea is to do this. Within the box (let's say it is defined between [-a,a] and within this region the hamiltonian is H={p^2}/{2m} so the solution is |\psi\rangle=c_+|p\rangle + c_- |-p\rangle. This approach is really the free particle, but I cannot work out how to adjust the potential for the momentum representation. Any help would be appreciated.
 
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You know the solutions to the free particle are e^{ipx}, so look for linear combinations of those such that they match the boundary conditions. If you are talking about a perfect box, then look for linear combinations such that the edges go to 0.
 
Fourier transform of the potential? It would be an oscillating and nasty thing. Also the boundary condition in the momentum space would be difficult to concider. Also remember that the momentum is not an eigenvalue for the bound problem (i.e., momentum and posistion are both uncertain).
The momentum operator is not hermitean either (->no real eigenvalues).
 

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