Group-velocity slowdown in a double quantum-dot molecule
  The slowdown of optical pulses due to quantum-coherence effects is investigated theoretically for an "active material" consisting of InGaAs-based double quantum-dot molecules. These are designed to exhibit a long lived coherence between two electronic levels, which is an essential part of a quantum coherence scheme that makes use of electromagnetically-induced transparency effects to achieve group velocity slowdown. We apply a many-particle approach based on realistic semiconductor parameters that allows us to calculate the quantum-dot material dynamics including microscopic carrier scattering and polarisation dephasing dynamics. The group-velocity reduction is characterized in the frequency domain by a quasi-equilibrium slow-down factor and in the time domain by the probe-pulse slowdown obtained from a calculation of the spatio-temporal material dynamics coupled to the propagating optical field. The group-velocity slowdown in the quantum-dot molecule is shown to be substantially higher than what is achievable from similar transitions in typical InGaAs-based single quantum dots. The dependences of slowdown and shape of the propagating probe pulses on lattice temperature and drive intensities are investigated. 
Stephan Michael, Weng W. Chow, Hans Christian Schneider
cond-mat.mes-hall physics.optics