The hermitian conjugate/adjoint -Quantum Physics

In summary, the hermitian conjugate of an operator, \hat{F}, written \hat{F}^{\tau} satisfies the condition:∫∅*(r)\hat{F}^{\tau}ψ(r)dr=(∫ψ*(r)\hat{F}∅(r)dr)*for any choice of wavefunctions ψ and ∅.
  • #1
Calcifur
24
2

Homework Statement



The hermitian conjugate of an operator, [itex]\hat{F}[/itex], written [itex]\hat{F}[/itex][itex]^{\tau}[/itex] satisfies the condition:

∫∅*(r)[itex]\hat{F}[/itex][itex]^{\tau}[/itex]ψ(r)dr=(∫ψ*(r)[itex]\hat{F}[/itex]∅(r)dr)*

for any choice of wavefunctions ψ and ∅. Show that:

([itex]\hat{F}[/itex]+i[itex]\hat{G}[/itex])[itex]^{\tau}[/itex]=[itex]\hat{F}[/itex][itex]^{\tau}[/itex] -i[itex]\hat{G}[/itex][itex]^{\tau}[/itex]

(10 marks)
2. The attempt at a solution

I feel like I'm missing something here, either that or the question's stupidly easily and isn't worth ten marks.
As ((A + B)* = A* + B*) and as with all complex conjugates (x+iy)*=(x-iy), it can be applied to the above as it's still just a complex conjugate. I know I'm supposed to use the condition above somehow so without obviously telling me the answer, could someone point me in the right direction for how I'm supposed to SHOW it please.
 
Last edited:
Physics news on Phys.org
  • #2
did you try using (F+iG) as an operator and then using the
∫∅*(r)Fˆτψ(r)dr=(∫ψ*(r)Fˆ∅(r)dr)* and seperating them while they are in (... )* and then apply
∫∅*(r)Fˆτψ(r)dr=(∫ψ*(r)Fˆ∅(r)dr)* in reverse way ? not sure but that may help.
 
  • #3
Hmmm. Yes, I can sort of see what you mean. I've tried it but I'm still confused with how the τ's are allowed to be separated. I think it's due to the question being worded in a confusing way. If I knew how operators could be manipulated algebraically then I'd probably get somewhere...I'm assuming they don't function like normal variables?
 
  • #4
∫∅*(r)(Fˆ+iGˆ)τψ(r)dr=(∫ψ*(r)(Fˆ+iGˆ)∅(r)dr)*
=(∫ψ*(r)(Fˆ)∅(r)dr+i∫ψ*(r)Gˆ(r)∅(r)dr)*
=((∫∅*(r)Fˆτψ(r)dr)*+i(∫∅*(r)Gˆτψ(r)dr)*)*
 
  • #5
crimsonidol said:
∫∅*(r)(Fˆ+iGˆ)τψ(r)dr=(∫ψ*(r)(Fˆ+iGˆ)∅(r)dr)*
=(∫ψ*(r)(Fˆ)∅(r)dr+i∫ψ*(r)Gˆ(r)∅(r)dr)*
=((∫∅*(r)Fˆτψ(r)dr)*+i(∫∅*(r)Gˆτψ(r)dr)*)*

Brilliant... I understand it now thanks crimsonidol!
 

1. What is the hermitian conjugate/adjoint in quantum physics?

The Hermitian conjugate, also known as the adjoint, is a mathematical operation in quantum physics that involves taking the complex conjugate of a matrix or operator and then transposing it. This operation is used to find the adjoint of an operator, which can be used to calculate the expectation value of a quantum mechanical observable.

2. How is the hermitian conjugate/adjoint related to the complex conjugate?

The hermitian conjugate/adjoint is closely related to the complex conjugate, as it involves taking the complex conjugate of a matrix or operator. However, the hermitian conjugate also involves transposing the matrix or operator, which makes it a more complex operation.

3. What are the properties of the hermitian conjugate/adjoint?

The hermitian conjugate/adjoint has several important properties in quantum physics. These include being linear, anti-linear, and involutive. This means that it follows the rules of linearity, anti-linearity, and self-inversion. Additionally, the hermitian conjugate of a product of two operators is equal to the product of their individual hermitian conjugates in reverse order.

4. How is the hermitian conjugate/adjoint used in quantum mechanics?

The hermitian conjugate/adjoint is used in quantum mechanics to calculate the expectation value of a quantum mechanical observable. This is done by taking the inner product of the state vector with the hermitian conjugate of the operator associated with the observable. The resulting complex number represents the expected measurement value of the observable.

5. What is the difference between the hermitian conjugate/adjoint and the transpose?

The hermitian conjugate/adjoint and the transpose are two different mathematical operations. While the transpose simply involves flipping the rows and columns of a matrix or operator, the hermitian conjugate also involves taking the complex conjugate of each element. Additionally, the transpose can only be applied to real numbers, while the hermitian conjugate can be applied to complex numbers as well.

Similar threads

  • Advanced Physics Homework Help
Replies
17
Views
1K
  • Advanced Physics Homework Help
Replies
4
Views
1K
  • Advanced Physics Homework Help
Replies
4
Views
3K
  • Advanced Physics Homework Help
Replies
1
Views
1K
Replies
7
Views
642
  • Advanced Physics Homework Help
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
25
Views
259
Replies
9
Views
38K
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Advanced Physics Homework Help
Replies
4
Views
963
Back
Top