Speaker: Ofer Firstenberg Affiliation: Technion-Israel Institute of Technology Title: Diffusion and Diffraction of Polaritons in Atomic Media Abstract: We investigate the non-local optical response in a medium of diffusing atoms. The two-photon spectra exhibit motional broadening and narrowing features along with a cusp-like or universal behavior. Accordingly, dark-state polaritons traversing the medium demonstrate a combined light-matter dynamics of atomic diffusion and optical diffraction. When taken out of resonance, the polaritons experience an additional 'motional-induced' diffraction, which we utilize to eliminate the total diffraction and diffusion of any arbitrary paraxial image propagating in the medium [1]. In this regime, narrow optical beams are two-dimensionally trapped by the diffusing atoms, in analogy to an optical trap of atoms. Further diffraction manipulation, such as directional biasing, doubling, and reversal, are also demonstrated. The latter manifests an effectively negative-index lens. Finally, we explore the coherent diffusion of spatial patterns using light storage. The interference of coherence is measured for patterns with non-uniform phase, and special transverse 'modes' are shown to expand or contract in a self-similar manner [2]. [1] O. Firstenberg, et al. Nat. Phys. 5, 665-668 (2009); [2] O. Firstenberg, et al. arXiv:1008.2654 (2010)