Coherently induced birefringence

Summary form only given. Quantum coherence phenomena offer a powerful method of controlling the optical properties of an atomic vapor, such as the absorption and refractive index. We demonstrate the use of quantum coherence to induce controllable birefringence in an atomic vapor and to thereby provide complete and efficient control over the polarization state of a probe laser beam propagating through the vapor. Quantum coherence has been previously observed to produce small polarization rotations, but these experiments suffered from significant absorption loss and produced rotations of at most a few degrees. Our experiments demonstrate the ability to induce linear or circular birefringence in an initially isotropic system that can be used to change the polarization state of a probe beam from linear to any desired polarization state with a total energy throughput greater than 97%.