Far-infrared-driven electron-hole correlations in a quantum dot with an internal tunneling barrier

Laser excited and FIR-driven, time-dependent electron-hole correlations in a prototypical GaAs quantum dot with an internal AlGaAs tunneling barrier are studied by numerical propagation of the time-dependent Schrödinger equation. The dimensions of the dot are $13\times 25\times 25{\mathrm{nm}}^3$ (denoted x, y, and z directions, respectively). The width of the symmetrically placed barrier in the x direction varies between 1 and 4 nm. The simulations, including a screened Coulomb interaction, time-propagates the electron-hole (exciton) wave function within the effective mass approximation. The Coulomb correlations are treated within the time-dependent configuration-interaction method. The hole mass is chosen to be heavy along the growth direction (x) and light in the lateral directions. The presence of the barrier allows the energy splittings of the excited states to be tuned for optimal correlation effects. Three cases illustrate how sequences of NIR and FIR pulses can excite and probe coherent correlation effects. Case I: A single FIR-coupled dark eigenstate can be used to modulate correlation induced beatings in a pair of optically excited eigenstates, but the beating is not significantly transferred into the dark state. Case II: With appropriate FIR pulse widths and center frequencies, a coherent optical excitation in a pair of correlation split states can be transferred unchanged into and out of a pair of optically dark states split by similar correlations. Case III: Correlations open new optical pathways that, for example, allow FIR pulses polarized in the x direction to transfer an excitonic excitation in x to an excitation in the perpendicular y and z directions.