Absorptive and dispersive optical responses of excitons in a single   quantum dot
  We have determined both the real and imaginary parts of the dielectric polarizability of a single quantum dot. The experiment is based on the observation and the manipulation of Rayleigh scattering at photon frequencies near the resonance of an optical exciton transition in single self-assembled InAs and InGaAs quantum dots. The interference between the narrow-band laser field and the weak electromagnetic field coherently scattered by the quantum dot is detected with a cryogenic Fabry-Perot setup by combined differential transmission and reflectivity measurements. 
B. Al\'en, A. H\"ogele, M. Kroner, S. Seidl, K. Karrai, R. J.   Warburton, A. Badolato, G. Medeiros-Ribeiro, P. M. Petroff