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conana
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Homework Statement
Two spin-1/2 particles are governed by [tex]\dfrac{J^2}{2I}+\omega_0 J_z[/tex] where [tex]J=J_1+J_2[/tex]. At time t = 0 the total angular momentum is measured and found to be 0.
(a) At time t, [tex]J_{1z}[/tex] is measured. What are the possible results and what is the probability of each?
Homework Equations
The Attempt at a Solution
So it seems that what I want to do is find [tex]|\psi (t)\rangle[/tex] in the eigenbasis of the hamiltonian, which would involve the total angular momentum of the two particles, j, and the z-component of the angular momentum, [tex]m_j[/tex], and then change to a basis involving the individual angular momenta so that I can find the possible results and probabilities for [tex]J_{z1}[/tex].
Since the total angular momentum was measured at t = 0, the system is in an eigenstate of the hamiltonian and, thus, the time evolution should not affect the probabilities at time t, so I can just look at [tex]|\psi (0)\rangle[/tex].
For 0 total angular momentum at t=0, it seems [tex]|\psi(0)\rangle=|0, 0\rangle[/tex] in the basis [tex]|j, m_j\rangle[/tex].
Now I run into a couple of problems.
(1) How can total angular momentum J = 0? If J = J1 + J2, then J1 + J2 = 0. It is my understanding that J1,J2 >=0 in general because J1 = L1 + S1 or abs(L1 - S1) (where L1 is the orbital angular momentum and S1 is the spin angular momentum, both of which are magnitudes i.e. > 0) and similarly for J2, so it must be that J1 = J2 = 0. For this problem, however, even if L1 = L2 = 0, it would be the case that J1 = J2 = 1/2 and thus J = 1. Is my understanding here totally flawed?
(2) Change of basis. I'm guessing I want to use a basis [tex]|j_1 m_1, j_2 m_2\rangle[/tex] where j1, j2 are the total angular momenta and m1, m2 are the z-component of angular momentum for particles 1 and 2, respectively. My professor gave us a table of Clebsch-Gordan coefficients for just such an occasion, but in this case I am not exactly sure how to apply it. I guess my problem is that I don't know how to find j1, j2 to be able to use the correct entry of my table. This stems, at least partly, from my first problem with the total J = 0.
This is part of a sample final exam question for my final exam tomorrow and, unfortunately, my professor is unavailable for help due to medical issues. Any help is GREATLY appreciated.