How is equation 4.61 derived from n dot s in the Arbitrary Spin Operator?

In summary, the conversation discusses the matrix definition for Sn (equation 4.61 on page 4) and a potential misunderstanding of the operator defined in equation 4.52. The participant eventually understands the concept after realizing their mistake.
  • #1
nateHI
146
4
http://www.tampa.phys.ucl.ac.uk/~tania/QM4226/SEC4B.pdf

At the above link, I'm not quite sure how the instructor got to the matrix definition for Sn(equation 4.61 on page 4) from n dot s. Does someone know of a link that doesn't skip that step?
 
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  • #2
nateHI said:
At the above link, I'm not quite sure how the instructor got to the matrix definition for Sn(equation 4.61 on page 4) from n dot s. Does someone know of a link that doesn't skip that step?

Well, n = (sin(theta) cos(phi), sin(theta) sin(phi), cos(theta)) is the radial versor, and the Pauli matrices (sigmax, sigmay, sigmaz) are the usual ones... take the scalar product... what don't you understand exactly?
 
  • #3
I'm not sure what the lower case s is, I think it should be upper case, i.e. the operator defined in eqn 4.52. The components of S are the pauli matrices times hbar/2 as in 4.55.
 
  • #4
OK I get it. It was a silly mistake. I was getting table 4.60 mixed up with the pauli matrices. Thanks.
 

1. What is an arbitrary spin operator?

The arbitrary spin operator is a mathematical representation of the spin of a quantum particle. It is used to describe the spin state of a particle, which is a fundamental property of particles that cannot be directly observed but has a significant impact on their behavior.

2. How is the arbitrary spin operator different from the spin operator?

The arbitrary spin operator is a generalization of the spin operator. While the spin operator is specific to particles with a spin of 1/2, the arbitrary spin operator can be used for particles with any spin value. It allows for a more comprehensive description of the spin state of a particle.

3. What is the significance of the arbitrary spin operator in quantum mechanics?

The arbitrary spin operator is essential in quantum mechanics as it helps describe the spin state of particles. It is used in many calculations and equations, such as the Schrödinger equation, to predict the behavior of quantum particles.

4. How is the arbitrary spin operator related to angular momentum?

The arbitrary spin operator is related to angular momentum as it is a component of the total angular momentum of a particle. The magnitude of the spin operator represents the spin angular momentum, while the direction of the operator represents the spin orientation.

5. Can the arbitrary spin operator be measured?

No, the arbitrary spin operator cannot be measured directly as it is a mathematical representation. However, the effects of the operator, such as the spin of a particle, can be measured through experiments and observations.

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