Substantial interaction between a singe atom and a focused light beam

We investigate both theoretically and experimentally the near-resonant interaction between a single atom in an optical dipole trap and a focused coherent light beam. We have demonstrated that even for a moderate focusing strength, a single atom localized at the focus of a simple aspheric lens can scatter a significant fraction of light[1,2], impose a phase shift~[3], and partially reflect a probe beam. With our current experimental system, we observe an extinction of 10\%, a phase shift of about 1$^\circ$ and a reflectivity of 0.17\%. For an optimal focusing geometry, we would expect an extinction up to 92\%, a phase shift of 30$^\circ$. The strength of the observed effect suggests that an efficient interface between atoms and photons for quantum information purposes can be established -- either without cavities, or by enhancing the electrical field in in a low-finesse cavity simply by strong focusing. We report on our experimental progress towards this goal. \\ {[1]} M. K. Tey, et al., Nature Physics {\bf 4} 924 (2008); {[2]} M. K. Tey et. al., New J. Phys. {\bf 11}, 043011 (2009); {[3]} S.A. Aljunid et al., Phys. Rev. Lett. {\bf 103}, 153601 (2009)