Single-atom detection in high-Q multimode cavities

We propose a new method for detecting and monitoring the motion of a single atom in high-Q optical resonators based on the position sensitive dispersi ve coupling of different field modes. Using sufficient atom-field detuning the irreversible evolution of the internal state and external motion of the atom can be kept small still allowing for a fast and reliable detection. A s an implementation we discuss the case of two counterpropagating modes in a microscopic ring resonator with spatially localized output coupler. The a nalytical estimates yielding 100% signal contrast for suitable parameters a re then confirmed by numerical solution of the time-dependent equations for the coupled atom-cavity dynamics. (C) 2000 Elsevier Science B.V. All right s reserved.