Fermi's golden rule derivation a bit hazy

In summary: The adjoint of ##e^{-i E_m t}## is ##e^{i E_m t}##, and this is why you get the required result. In summary, the issue was related to hermiticity and adjointing, and the solution was to focus on the expression ##e^{i H_0 t}## and its adjoint.
  • #1
Replusz
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TL;DR Summary
I am stuck between line 1 and 2 in the derivation below. I have attached what I tried
1586805944414.png

1586806504002.png

1586806124910.png
My thought is following:
1586806435700.png

However this would give me w=E_m + E_n instead of E_m-E_n
I guess something relating to hermiticity or adjointing something has gnoe wrong in my version.
Can someone point me in the right direction please? :)
Thank you in advance!
 
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  • #2
Replusz said:
However this would give me w=E_m + E_n instead of E_m-E_n

Are you sure you didn't get ##\omega = -\left(E_m + E_n \right)##? Then I would have replied that, in Dirac notation, the bra - ket is conjugate linear in the bra, i.e., if you pull a scalar outside of the bra, you have to take the complex conjugate of the scalar.

I do get the required result.
 
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  • #3
Replusz said:
Summary:: I am stuck between line 1 and 2 in the derivation below. I have attached what I tried

View attachment 260581
View attachment 260585
View attachment 260582My thought is following:
View attachment 260584
However this would give me w=E_m + E_n instead of E_m-E_n
I guess something relating to hermiticity or adjointing something has gnoe wrong in my version.
Can someone point me in the right direction please? :)
Thank you in advance!
I agree with George. Focus on your ##e^{i H_0 t}## which you turned into ##e^{-i E_m t}##.
 
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  • #4
nrqed said:
I agree with George. Focus on your ##e^{i H_0 t}## which you turned into ##e^{-i E_m t}##.

So ##<m|e^{i H_0 t} = adjoint(e^{-i H_0 t} |m> ) = adjoint(e^{-i E_m t} |m> ) = e^{ i E_m t} <m| ##

Is this correct?
(if this is correct then everything makes sense)
 
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  • #5
Replusz said:
So ##<m|e^{i H_0 t} = adjoint(e^{-i H_0 t} |m> ) = adjoint(e^{-i E_m t} |m> ) = e^{ i E_m t} <m| ##

Is this correct?
(if this is correct then everything makes sense)
Yes, this is correct.
 
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What is Fermi's golden rule?

Fermi's golden rule is a fundamental principle in quantum mechanics that describes the transition rate between two quantum states. It states that the transition rate is proportional to the square of the matrix element of the perturbation between the initial and final states.

Why is the derivation of Fermi's golden rule hazy?

The derivation of Fermi's golden rule can be hazy because it involves complex mathematical concepts and equations that may be difficult to understand without a strong background in quantum mechanics and mathematics. Additionally, there are multiple approaches to deriving the rule, which can lead to confusion.

What are some common misconceptions about Fermi's golden rule?

One common misconception about Fermi's golden rule is that it only applies to simple systems and cannot be used for more complex systems. However, the rule can be applied to a wide range of systems, as long as the perturbation is small enough.

Another misconception is that Fermi's golden rule only applies to transitions between discrete energy levels. In reality, it can also be used to describe transitions between continuous energy levels.

How can one better understand the derivation of Fermi's golden rule?

To better understand the derivation of Fermi's golden rule, it is important to have a strong understanding of the underlying mathematical concepts and equations involved. It can also be helpful to consult multiple sources and seek guidance from a knowledgeable instructor or mentor.

What are some practical applications of Fermi's golden rule?

Fermi's golden rule has many practical applications in physics, chemistry, and engineering. It is commonly used to study the rates of chemical reactions, the behavior of electrons in materials, and the emission and absorption of radiation. It is also used in the development of quantum technologies such as quantum computing and quantum cryptography.

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