Describing the microscopic details of the interaction of magnets and spin-polarized currents is key to achieving control of such systems at the microscopic level. Here we discuss a description based on the Keldysh technique, casting the problem in the language of open quantum systems. We reveal the origin of noise in the presence of both fieldlike and dampinglike terms in the equation of motion arising from spin conductance.
Tassi, C., Barbieri, M., Raimondi, R. (2019). Quantum noise in the spin transfer torque effect. PHYSICAL REVIEW. B, 100(18) [10.1103/PhysRevB.100.184418].