Light switching at low light level based on changes in light polarization.

We studied the polarization spectroscopy of a linearly-polarized optical (probe) field in a multi-Zeeman-sublevel atomic system of the 87Rb D1 line. The polarization spectroscopy signals of the probe light result from the changes in its polarization, which are caused by a left-circularly polarized pumping beam. A theoretical analysis involving multiple Zeeman sublevels is presented and the results are in qualitative agreement with the experimental observations. Based on this phenomenon, we demonstrated a light switch at low light level ([?]68 photons per l2/2p) with a switching efficiency of [?]3%. [ABSTRACT FROM AUTHOR]