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Homework Statement
The problem is as follows. I have two spins, [itex]m_S[/itex] and [itex]m_I[/itex]. The first spin can either be [itex]\uparrow[/itex] or [itex]\downarrow[/itex] , and the second spin can be -1, 0 or 1.
Now, I envision the situation as the first spin being on the bloch sphere, with up up to and down at the bottom.
What I want to do is as follows:
Given an initial situation [itex]\left|\psi\right> = \left|\psi_1\right> \otimes \left|\psi_2\right> = \left|\uparrow\right> \otimes \frac{1}{\sqrt{3}}\left( \left|-1\right> + \left|0\right>+ \left|1\right> \right)[/itex]
I want to rotate m_S around the x-axis by pi/2, followed by a waiting time t. In this waiting time t, I want m_S to rotate around the z-axis, conditional on the state of m_I. If m_I is -1, m_S should rotate clockwise, if it is 0, m_S should not rotate, and if it is 1, m_S should rotate anticlockwise.
After this has happened, I want to perform another rotation, this time around the y-axis. This way, the state of m_S becomes entangled with the state m_I.
The Attempt at a Solution
Now, the rotation part I know how to do, as that can simply be written as
[itex]\left|\psi\right> = R_x (\frac{\pi}{2}) \left|\psi_1\right> \otimes \left|\psi_2\right> = \frac{1}{\sqrt{2}} \left( \left|\uparrow\right> -i \left|\downarrow\right> \right) \otimes \frac{1}{\sqrt{3}}\left( \left|-1\right> + \left|0\right>+ \left|1\right> \right)[/itex]
But here I get to the point of the conditional rotation, and I don't know how to proceed. Could anyone help me start with this?
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