# Arbitrary spin operator

1. Sep 29, 2010

### nateHI

http://www.tampa.phys.ucl.ac.uk/~tania/QM4226/SEC4B.pdf [Broken]

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?

Last edited by a moderator: May 5, 2017
2. Sep 29, 2010

### Petr Mugver

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. Sep 29, 2010

### t_barlow

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. Sep 29, 2010

### nateHI

OK I get it. It was a silly mistake. I was getting table 4.60 mixed up with the pauli matrices. Thanks.

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