Cavity QED with high-Qwhispering gallery modes

We report measurements of cavity-QED effects for the radiative coupling of atoms in a dilute vapor to the external evanescent field of a whispering-gallery mode (WGM) in a fused silica microsphere. The high $Q$ $(5\mathrm{}\times {10}^7)$, small mode volume (10${}^{-8}$ cm${}^3)$, and unusual symmetry of the microcavity evanescent field enable velocity-selective interactions between fields with photon number of order unity in the WGM and $N_T\sim 1$ atoms in the surrounding vapor.