Phonon-assisted population inversion of a single quantum dot
  We demonstrate an approach to realize the population inversion of a single InGaAs/GaAs quantum dot, which is driven by a laser pulse tuned within the neutral exciton phonon sideband. The inversion is achieved by rapid thermalization of the optically dressed states via phonon-assisted relaxation. A maximum exciton population of 0.67 $\pm$ 0.06 is measured for a laser tuned 0.83 meV to higher energy and the phonon sideband is mapped using a two-color pump-probe technique. Our experiments reveal that, in accordance with theory, the phonon-bath provides additional functionality for an optically driven quantum dot qubit. 
J. H. Quilter, A. J. Brash, F. Liu, M. Gl\"assl, A. M. Barth, V. M.   Axt, A. J. Ramsay, M. S. Skolnick, A. M. Fox
cond-mat.mes-hall