Dispersive Optical Interface Based on Nanofiber-Trapped Atoms
  We dispersively interface an ensemble of one thousand atoms trapped in the evanescent field surrounding a tapered optical nanofiber. This method relies on the azimuthally-asymmetric coupling of the ensemble with the evanescent field of an off-resonant probe beam, transmitted through the nanofiber. The resulting birefringence and dispersion are significant; we observe a phase shift per atom of $\sim$\,1\,mrad at a detuning of six times the natural linewidth, corresponding to an effective resonant optical density per atom of 0.027. Moreover, we utilize this strong dispersion to non-destructively determine the number of atoms. 
S. T. Dawkins, R. Mitsch, D. Reitz, E. Vetsch, A. Rauschenbeutel
quant-ph physics.atom-ph physics.optics