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 polarization dephasing dynamics. The group-velocity reduction is characterized in the frequency domain by a quasiequilibrium slowdown factor and in the time domain by the probe-pulse slowdown obtained from a calculation of the spatiotemporal 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 dependencies of slowdown and shape of the propagating probe pulses on lattice temperature and drive intensities are investigated.