Coherent control of the polarization of an optical field

Through use of quantum coherence in an atomic system, we demonstrate that an optical field can be used to completely control the polarization state of another field. Theoretical and experimental results show that by applying a field with a frequency tuned near one transition, an initially isotropic atomic vapor can be made to behave as a linearly or circularly birefringent material for fields tuned near an adjoining transition. [S0031-9007(98)07434-1].