Nonlinear Faraday rotation and detection of superposition states in cold atoms

Abstract

We report on the observation of nonlinear Faraday rotation with cold atoms at a temperature of $~100$ $\ensuremath{\mu}$K. The observed nonlinear rotation of the light polarization plane is up to $0.1$ rad over the $1$-mm-size atomic cloud in approximately $10$-mG magnetic field. The nonlinearity of rotation results from long-lived coherence of ground-state Zeeman sublevels created by a near-resonant light. The method allows for creation, detection, and control of atomic superposition states. It also allows applications for precision magnetometry with high spatial and temporal resolution.