My question comes from a small section about Wigner's experiment in the book 'The Interpretation of Quantum Mechanics' by Roland Omnes. I've attached two pages below to show what I'm referencing.

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My question is simply about the diagram shown on the first page.

In the text it states that we fire an atom with its spin aligned along the x-direction through a Stern-Gerlach magnet directed along the z-direction.

In the original Stern-Gerlach experiment, the spin is parallel (or anti-parallel) to the (non-uniform) magnetic field which results in a deflection of the path. From what I understand, the deflection of path comes from the spin (or magnetic moment) component of the atom being parallel with the magnetic field from the magnet (because the interaction energy of the magnetic moment associated with the spin is proportional to the dot product of the spin and magnetic field), which results in a force causing the atom to change its direction.

However, in this Wigner's thought experiment, the spin of the atom and magnetic field of the magnet are perpendicular yet the diagram still shows that there is still a deflection of the path. I thought that the spin direction/component and the magnetic field had to be parallel in order for this deflected path. Why does the diagram still show a deflection in this case?



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