Nonlinear optical microscopy of a single self-assembled InGaAs quantum dot

Semiconductor quantum dots (QDs) exhibit exciting prospects for solid state qubits. Here we present the first ultrafast all-optical scheme for manipulation and read-out of a single QD and, thereby, pave the way towards a variety of such quantum coherent studies. A single InGaAs/GaAs QD is isolated by an aluminum shadow mask of 450 nm diameter. Optical excitation and read-out is achieved in a nondegenerate pump-probe scheme. Carriers are generated in the wetting layer beneath the QD with a 100 fs pump pulse and captured into the QD. The excitation induced transmission changes are analyzed over a broad range of probe wavelengths and various delay times. In particular, we identify signatures of the single exciton transition at EX=1.374 eV and transitions of several multi-exciton complexes. These bleaching signals are in the order of ΔT/T ∝10-5 and reveal a picosecond dynamics likely related to intra-QD carrier relaxation. In the next step, we will analyze QDs with excitonic transitions around 1.3 eV which are characterized by a larger confinement potential and better optical quality. To this end, we have developed a novel femtosecond Ti:Sapphire oscillator that, remarkably, provides ∝30 fs pulses tunable to wavelengths as long as 970 nm