Rotation Operator Matrix Representation using |+z> and |-z> Basis

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Homework Help Overview

The discussion revolves around determining the matrix representation of the rotation operator \( R(\phi k) \) using the states \(|+z\rangle\) and \(|-z\rangle\) as a basis. Participants are exploring how to express the operator in matrix form and verify the property \( R^{\dagger}R=1 \).

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the need to express \( R|\psi\rangle \) in terms of a matrix and consider how to operate \( R \) on a state expressed as a linear combination of the basis states. There are questions about the relationship between the rotation operator and the Pauli spin matrices. One participant mentions using a rotation matrix if the matrix is not in the \( z \) basis.

Discussion Status

Some participants have provided guidance on using the spin operators as generators of rotations, while others are clarifying their understanding of the notation and the derivation of the transformation matrix \( S \). There is an ongoing exploration of the concepts involved without a clear consensus on the best approach.

Contextual Notes

Participants are navigating the complexities of changing bases and the implications of using different representations for the rotation operator. There is uncertainty regarding the derivation of the transformation matrix \( S \) and its application in this context.

cragar
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Homework Statement


Determine the matrix representation of the rotation operator
R(\phi k) using the states |+z> and |-z> as a basis. Using your matrix representation verify that R^{\dagger}R=1

The Attempt at a Solution


Do I need to write R| \psi> in terms of a matrix.
If I have |\psi>=a|+z>+b|-z>
Then do I just operate R on \psi and then write this in terms of a matrix.
are these related to the Pauli spin matrices
 
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cragar said:

Homework Statement


Determine the matrix representation of the rotation operator
R(\phi k) using the states |+z> and |-z> as a basis. Using your matrix representation verify that R^{\dagger}R=1

The Attempt at a Solution


Do I need to write R| \psi> in terms of a matrix.
If I have |\psi>=a|+z>+b|-z>
Then do I just operate R on \psi and then write this in terms of a matrix.
I'm not sure exactly what you had in mind, but it's probably not the most straightforward way to solve this problem.
are these related to the Pauli spin matrices
Yes. Remember that the spin operators ##\hat{S}_x##, ##\hat{S}_y##, and ##\hat{S}_z## are generators of rotations. (This is definitely covered in your textbook.) Use that fact to calculate R.
 
ok thanks for your help. My book gives the matrix for R and it is in the z basis.
And I took R^{\dagger}R and it equaled one. But If the matrix wasn't in the
z basis would I use the roatation matrix to get the answer.
I would take S^{\dagger}RS and this would give the correct R for the problem.
 
I don't understand what you're asking. Well, I sort of do, but I'd like you to clarify your question. What is S? How did you find S?
 
s= \[left (begin{array}{cc}<+z|+x>& <+z|-x>\\ <-z|+x>& <-z|-x> \end{array}\right)\]
where the bras are what basis I am going to and the kets are the basis that I was in. I don't really know how S is derived though
 
Last edited:
Yes, that's the regular method you use to change bases. You're doing the same thing you learned in linear algebra. It's just the notation that's different.
 

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