Matrix representation in QM Assignment -- Need some help please

In summary, the conversation discusses the use of eigenstates |z+⟩ and |z−⟩ of Sz^ in constructing matrices for spin operators Sx^, Sy^, and Sz^. The question also asks for the construction of matrices for spin operators using eigenstates |x+⟩ and |x−⟩ of Sx^. The relevant equations and the original assignment statement are provided. The solution provided uses the relationship between x and z to evaluate the Sx operator in matrix form. The person also asks for help in evaluating Sy and Sz operators for spin.
  • #1
Ashish Somwanshi
31
4
Homework Statement
In the lecture, we used the eigenstates |z+⟩ and |z−⟩ of Sz^, we obtained the matrices for spin operators

Sx^=ℏ/2(0,1,1,0) Sy^=ℏ/2(0,i,−i,0) Sz^=ℏ/2(1,0,0,−1)
note: the numbers in brackets are 2×2 matrices!!!


Now use the eigenstates of |x+⟩ and |x−⟩ of Sx^,as a new basis, construct matrices for the spin operators Sx^, Sy^ and Sz^.
Relevant Equations
Both Question and Relevant equations are posted below in attempt.
This screenshot contains the original assignment statement and I need help to solve it. I have also attached my attempt below. I need to know if my matrices were correct and my method and algebra to solve the problem was correct...
Screenshot_20221008_235549.jpg
 

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  • #2
Ashish Somwanshi said:
Homework Statement:: In the lecture, we used the eigenstates |z+⟩ and |z−⟩ of Sz^, we obtained the matrices for spin operators

Sx^=ℏ/2(0,1,1,0) Sy^=ℏ/2(0,i,−i,0) Sz^=ℏ/2(1,0,0,−1)
note: the numbers in brackets are 2×2 matrices!Now use the eigenstates of |x+⟩ and |x−⟩ of Sx^,as a new basis, construct matrices for the spin operators Sx^, Sy^ and Sz^.
Relevant Equations:: Both Question and Relevant equations are posted below in attempt.

I have also attached my attempt below.
Please make it a habit to post your work using LaTeX, and not in blurry attached pictures. There is a "LaTeX Guide" link below the Edit window to help you learn LaTeX. Thank you.
 
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  • #3
My solution to above assignment goes like this:

Since
| ×±> = 1/ sqrt(2) |z+> ± 1/sqrt(2) |z->

|x+> = 1/sqrt (2) |z+> + 1/sqrt(2) |z->
|x-> = 1/sqrt(2) |z+> - 1/sqrt(2) |z->

So eigenvalue equations are:

Sx |x+> = 1/sqrt(2) { |z+> + |z->}
Sx |x-> = 1/sqrt(2) { |z+> - |z->}

So we can represent Sx operator in matrix form as:

Sx = 1/sqrt(2)*
|z+> + |z->0
0|z+> - |z->

Is my method to evaluate Sx operator from the relationship between x and z correct? Also how can I evaluate Sy and Sz operators for spin.?
 
Last edited:

1. What is matrix representation in quantum mechanics?

Matrix representation in quantum mechanics is a mathematical tool used to represent quantum states and operators in a matrix form. This allows for easier manipulation and calculation of quantum systems.

2. How is matrix representation used in quantum mechanics?

Matrix representation is used to represent quantum states, operators, and observables in a matrix form. This allows for easier calculation of quantum systems and prediction of their behavior.

3. What are the advantages of using matrix representation in quantum mechanics?

Matrix representation allows for easier manipulation and calculation of quantum systems, as well as the ability to easily combine and transform operators. It also provides a visual representation of quantum states and operators, making it easier to understand and analyze complex quantum systems.

4. How do you convert a wavefunction to matrix representation?

To convert a wavefunction to matrix representation, you first need to choose a basis set and represent the wavefunction as a linear combination of basis states. Then, the coefficients of the basis states become the elements of the matrix representation.

5. Can matrix representation be used for all quantum systems?

Yes, matrix representation can be used for all quantum systems. However, the size and complexity of the matrices may vary depending on the system and the chosen basis set.

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