Quantum Mechanics
Stern-Gerlach: Electrons

An electron beam passing through a Stern-Gerlach device does not separate into spin-up and spin-down components. The spreading of the electron wave packet washes out the separation effect due to the electron spin. For an inhomogeneous magnetic field of the form B = B_0 (0,0,y), the motion of the particle is in the xy - plane. The effect of the Lorentz force is masked by the spreading of the electron wave packet.

Superposition of wave packets with spin up and spin down moving in an inhomogeneous magnetic field perpendicular to the plane of motion.