Ultrafast coherent control of excitons and exciton-polaritons in quantum nanostructure

We have demonstrated ultrafast coherent control of excitons and exciton-polaritons in semiconductor quantum nanostructures. An InGaAs/AlGaAs multi-quantum-well Bragg structure and an AlGaAs/GaAs crescent-shaped quantum wire structure were used as samples for the control of the exciton-polariton and excitons in the nanostructure. In the multi-quantum-well Bragg sample, a two-stage decay due to the super-radiant exciton-polariton mode is clearly observed under the resonance conditions. Highly sensitive coherent control measurement enables us to observe the dephasing characteristics in the crescent-shaped quantum wire sample, and a very fast dephasing time T-2 of between 200 fs and 300 fs with powder dependence was observed.