A problem of momentum representation

In summary, the conversation discusses proving a specific equation using the commutator and distributional extensions. The commutator is used to determine the relationship between two operators, while the distributional extensions are used in the proof. The conversation also includes a hint to evaluate a specific equation and use a given fact to arrive at the desired result. There is disagreement on the validity of using the commutator in this proof.
  • #1
fish830617
1
0
Given
[x,p] = i * h-bar,
prove that
<p|X|p'> = [i * h-bar / (p' - p)] * δ(p - p').

I don't understand why commutator matters with this proof?
 
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  • #2
The commutator tells you what the relationship between p and x is. You are not supposed to use explicit realizations of x or p, but only the commutator.

Cheers,

Jazz
 
  • #3
This is nonsense. The commutator is defined for the H-space operators, the thing you got to prove is for their distributional extensions.
 
  • #4
And what's written is not even true for the distributional extensions.
 
  • #5
fish830617 said:
Given
[x,p] = i * h-bar,
prove that
<p|X|p'> = [i * h-bar / (p' - p)] * δ(p - p').

I don't understand why commutator matters with this proof?

Hint: try evaluating <p|[X,p]|p'>, and use the fact (not given, but based on the result this is how |p> is normalized) that <p|p'>= δ(p - p').
 
  • #6
dextercioby said:
This is nonsense. The commutator is defined for the H-space operators, the thing you got to prove is for their distributional extensions.

I don't understand how is this a nonsense? I mean we can arrive at second equation (with minor correction) starting from commutation relation and certain assumptions. Can't we?
 

FAQ: A problem of momentum representation

What is momentum representation?

Momentum representation is a mathematical tool used in quantum mechanics to describe the state of a particle in terms of its momentum rather than its position. It is often used in conjunction with position representation to provide a more complete picture of a particle's state.

Why is momentum representation important?

Momentum representation is important because it allows us to understand the behavior of particles at the quantum level. It is also a useful tool for solving certain problems in quantum mechanics, such as calculating the probability of a particle to have a certain momentum.

What is the relationship between momentum representation and position representation?

Momentum representation and position representation are two different mathematical representations of the same physical system. Momentum representation uses the momentum of a particle to describe its state, while position representation uses the position of a particle. They are related through a mathematical transformation known as a Fourier transform.

How does momentum representation differ from classical mechanics?

In classical mechanics, particles are described using their position and momentum in terms of classical variables, such as position and velocity. In momentum representation, particles are described using quantum variables, such as wave functions and operators, which take into account the probabilistic nature of quantum systems.

Can momentum representation be used for all types of particles?

Yes, momentum representation can be used for all types of particles, including elementary particles such as electrons and protons, as well as larger particles like atoms and molecules. It is a fundamental tool in quantum mechanics and is applicable to all quantum systems.

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