Photon-Mediated Interaction between Two Distant Atoms
  We study the photonic interactions between two distant atoms which are coupled by an optical element (a lens or an optical fiber) focussing part of their emitted radiation onto each other. Two regimes are distinguished depending on the ratio between the radiative lifetime of the atomic excited state and the propagation time of a photon between the two atoms. In the two regimes, well below saturation the dynamics exhibit either typical features of a bad resonator, where the atoms act as the mirrors, or typical characteristics of dipole-dipole interaction. We study the coherence properties of the emitted light and show that it carries signatures of the multiple scattering processes between the atoms. The model predictions are compared with the experimental results in J. Eschner {\it et al.}, Nature {\bf 413}, 495 (2001). 
Stefan Rist, J\"urgen Eschner, Markus Hennrich and Giovanna Morigi