  We present a theory of magnetization dynamics driven by spin-polarized
current in terms of the quantum master equation. In the spin coherent state
representation, the master equation becomes a Fokker-Planck equation, which
naturally includes the spin transfer and quantum fluctuation. The current
electron scattering state is correlated to the magnet quantum states, giving
rise to quantum correction to the electron transport properties in the usual
semiclassical theory. In the large spin limit, the magnetization dynamics is
shown to obey the Hamilton-Jacobi equation or the Hamiltonian canonical
equations.
