Temporal Sorting of Optical Multiwave-Mixing Processes in Semiconductor Quantum Dots

Interaction of light with atomic-like solid-state systems, such as semiconductor quantum dots (QDs) with discrete energy levels, is key for the implementation of high-speed quantum gates and information processing in semiconductor-based devices. Of particular interest are degenerate multiwave-mixing processes under resonant conditions that establish strong light-matter interactions beyond the limits of perturbative nonlinear optics. Here, we exploit a multitude of picosecond optical pulses to manipulate the unitary evolution of excitons in (In,Ga)As QDs and address the role of resonance detuning in an inhomogeneously broadened ensemble. In particular, we use the two-pulse photon echo sequence to uncover the coherent dynamics of charged excitons, whereas the areas of two additional control pulses serve as tuning knobs for adjusting the magnitude and timing of the coherent emission in a wide range up to several hundred of picoseconds. Furthermore, we make use of the spin degeneracy of the ground and excited states of charged QDs to control the polarization state of the emitted light. We reveal that control pulses, whose durations are comparable to the dephasing time of the ensemble, lead to a temporal sorting of optical multiwave-mixing processes, which is in accordance with the developed theoretical model. Lifting the temporal degeneracy allows us to smoothly trace the transition from the perturbative to the regime of Rabi rotations and opens up new possibilities for the optical investigation of complex energy-level structures in so far unexplored material systems.