Cavity QED with high-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Q</mml:mi></mml:math>whispering gallery modes

Abstract

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 $Q$ $(5\ifmmode\times\else\texttimes\fi{}{10}^{7})$, small mode volume (10${}^{\ensuremath{-}8}$ 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 ${N}_{T}\ensuremath{\sim}1$ atoms in the surrounding vapor.