Temporal Oscillations of Nonlinear Faraday Rotation in Coherently Driven Media

New phenomenon of temporal oscillations of nonlinear Faraday rotation in a driven four-level system is predicted. We show that in this system with one upper level, under the conditions of electromagnetically induced transparency created by a strong coupling field, the polarization rotation of weak probe light exhibits slowly damped oscillations with a frequency proportional to the strength of an applied magnetic field. This opens up an alternate way to sensitive magnetometric measurements. Applications in low-light nonlinear optics such as photon entanglement are feasible.