Measurement of optical absorption by a single quantum dot exciton

We have measured the optical absorption due to an exciton confined to a single interface fluctuation quantum dot by directly measuring the transmission through both a submicron aperture and near-field microscopy. The measurements reveal large dipole moments approaching 100 D at 6 K. These results are compared to theoretical predictions based on a physical size estimated from photoluminescence excitation spectroscopy. The very large dipole moment makes these quantum dots attractive candidates for use in microcavities and quantum logic gates.