Deriving Transition Amplitude: Hamiltonian & $\psi_0 \to \psi_1$

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Discussion Overview

The discussion revolves around the derivation of the transition amplitude from one quantum state |\psi_0\rangle to another |\psi_1\rangle, as presented in Peskin & Schroeder. Participants explore the relationship between the Hamiltonian operator and the transition probability, as well as the role of the unitary time evolution operator in quantum mechanics.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant cites Peskin & Schroeder's formula for transition probability as given by the Hamiltonian: \(\langle \psi_1|H|\psi_0\rangle\).
  • Another participant suggests that the question indicates a lack of familiarity with basic quantum mechanics, implying that the original poster may not be ready for the material in Peskin & Schroeder.
  • A participant mentions having read Griffiths but acknowledges a potential oversight regarding the derivation of the transition amplitude.
  • One participant emphasizes that understanding this concept is fundamental to quantum mechanics and suggests revisiting foundational texts like Griffiths or Schiff.
  • Another participant introduces the unitary time evolution operator \(U\), which is expressed as an exponential of the Hamiltonian, as a common alternative formulation for transition amplitudes.
  • This participant also expresses interest in checking Schiff for equivalence between the formulations discussed.

Areas of Agreement / Disagreement

There appears to be disagreement regarding the foundational knowledge required to understand the transition amplitude. Some participants assert that the concept is basic, while others suggest that the original poster may need to review earlier material. Additionally, there are competing views on the use of the Hamiltonian versus the unitary time evolution operator in expressing transition amplitudes.

Contextual Notes

Some participants reference different quantum mechanics textbooks, indicating varying levels of detail and approaches to the topic. The discussion does not resolve whether the Hamiltonian formulation and the unitary operator formulation are equivalent, nor does it clarify the assumptions underlying the transition amplitude derivation.

Identity
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I'm reading through Peskin&Schroeder, and they mention that the probability of transition from a state [itex]|\psi_0\rangle[/itex] to a state [itex]|\psi_1\rangle[/itex] is given by:
[tex]\langle \psi_1|H|\psi_0\rangle[/tex]
where [itex]H[/itex] is the Hamiltonian. Can someone please explain how this formula is derived? Thx
 
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This is very basic QM.

I'm afraid that if this isn't immediately obvious to you, Peskin and Schroeder is too advanced for you. Have you taken undergrad QM? What book did you use?
 
Well, I've read most of Griffiths, but I think it may have been something I overlooked. Can you tell me? Thx
 
It's not something you overlook. This is one of the most basic aspects of quantum mechanics. I don't have Griffiths nearby, but Schiff devotes about 150 pages to this. If this isn't second nature to you, you aren't ready for Peskin & Schroeder. You'd be better served to go back to Griffiths and understand it before trying to move on.
 
Maybe this is an equivalent formulation, but I've usually seen a unitary time evolution operator U which is an exponential of the Hamiltonian operator, not the Hamiltonian operator itself, being used in expressing the amplitude.
 
lugita15 said:
Maybe this is an equivalent formulation, but I've usually seen a unitary time evolution operator U which is an exponential of the Hamiltonian operator, not the Hamiltonian operator itself, being used in expressing the amplitude.

Yes, I've seen it in this form
[tex]|\psi\rangle = e^{-i\frac{H}{\hbar}t}|\psi(0)\rangle[/tex]

I may look at Schiff to see if it is an equivalent formulation
 

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