Group-velocity slowdown in a double quantum dot molecule

Abstract

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 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.

Microscopic model for intersubband gain from electrically pumped quantum-dot structures

“…Thus, for the same inversion N , the gain on the intersubband transition is larger than that on an interband transition in the QD. The choice of the polarization dephasing of γ d = 1.0 meV is motivated by the restrictions that it has to be higher than intersubband dephasing for the case of unpopulated QD scattering states and a small carrier density in the QWs ( γ d < 0.1 meV), 50 but lower than an interband dephasing with an appreciable population in the QD scattering states ( γ d up to 10 meV). 56 We will plot the small signal gain in addition to the inversion between the optically active states in the following.…”

“…Thus, we follow Ref. 50 and introduce an effective quasi-particle broadening for the scattering contributions. By using an effective quasi-particle broadening we work with polarons, i.e., quasi-particles that include the effect of the coupling to phonons, instead of the "naked" QD electronic levels.…”

“…We have determined this broadening from single-pole approximations to the zero-density QD polaronic spectral functions, see also in Ref. 50, in the style of Ref. 51 and 52 and neglected the Coulomb-interaction contribution to the effective quasiparticle broadening.…”

“…This incorporation is done by following Ref. 50 for the derivation of the electron-phonon and electron-electron scattering. In contrast to Ref.…”

Linear and nonlinear tunable optical properties of intersubband transitions in GaN/AlN quantum dots in presence and absence of wetting layer

“…Also they have found that coulomb interactions shift the molecular resonance of charged exciton with respect to the single charge, enabling the QDs lightinduced coupling. Theoretically, Michael et al [9] explored the slowdown of optical pulses due to the quantum coherence effects for an active material consisting of double InGaAs-based QD molecules. Also the dependencies of slowdown, the shape of propagating probe pulses on lattice temperature and drive intensities have been explored as well.…”