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HL: Halbleiterphysik
HL 27: Ultrakurzzeitph
änomene II
HL 27.12: Talk
Wednesday, March 13, 2002, 17:15–17:30, H14
Ultrafast near-field spectroscopy of single quantum dots — •Kerstin Mueller1, Tobias Guenther1, Christoph Lienau1, Thomas Elsaesser1, Soheyla Eshlaghi2, and Andreas Wieck2 — 1Max-Born-Institut, Max-Born-Str. 2A, 12489 Berlin — 2Ruhr-Universitaet Bochum, D-44870 Bochum
Quantum dots (QD) formed by interface fluctuations of thin quantum wells (QW) serve as important models of arti-ficial solid state atoms. This makes them interesting as basic units for quantum information processing but also as probes of the dynamics of wavefunction localization in disordered media [1]. Such applications rely on the ability to probe and control coherences in these systems on ultrafast time scales shorter than their dephasing times. We report the first ultrafast study of the nonlinear optical response of a single QD. We demonstrate that transient differential reflectivity spectra show pronounced oscillatory structures around the ground state QD absorption reso-nance. These oscillations persist up to negative delay times of more than 10 ps and reflect the perturbed free induc-tion decay of the coherent polarization of a single exciton. Both the temporal and spectral evolution of the differen-tial reflectivity point to a transient QD nonlinearity which is not accounted for by simple Pauli blocking and differs from that of atomic systems. Contributions of polarization scattering, as known from quantum wells, and population relaxation will be discussed and compared to a detailed theoretical model. [1] F. Intonti et al., Phys. Rev. Lett. 87, 076801 (2001).