Coherent control of photo-excited carriers in semiconductor quantum dots using near-field scanning optical microscope

应变驱动的半导体量子点（SAQD）的自组装提供了在所有三个维度上的纳米级载流子限制。SAQD的一个迷人的特性是它们具有大能级间距的离散态密度（DOS），与高维结构相比，其中声学声子介导的散射应该被抑制。因此，SAQD中的激子有望表现出较长的相干时间，这对于量子信息处理的应用是有利的。在能级间弛豫方面，与纵光学（LO）声子的相互作用是SAQD的一个重要方面。这些声子介导的转变可以在单点光致发光激发（PLE）光谱中得到证实，其中弛豫路径的减少使得单个LO声子在基态发射中可见。到目前为止，已经清楚地观察到几个LO声子相关的过渡，包括体GaAs。在能量区域高于 ...更多信息 1LO，单点PLE光谱揭示了一些强烈的PLE功能，被认为是2LO声子共振。由于激子激发态的存在，在2LO区域存在着几种性质不同的弛豫路径。在不同的激发功率条件下，几个2LO共振在峰中出现凹陷结构。所观察到的倾角结构表明线加宽，即使在个别的共振线。相反，相应的双激子共振仍然有尖锐的峰值，表明2LO共振由几个弛豫通道与不同的散射过程。这些观察结果可以解释为什么PLE共振即使在单个SAQD中也表现出短的退相时间。此外，我们发现声子介导的跃迁可以很大程度上消除双色激发PLE光谱。谱线展宽的减少表明，PLE包括一些声子相关的跃迁与大的弛豫窗口。少

The strain-driven self-assembly of semiconductor quantum dots (SAQDs) provides nanometer scale carrier confinement in all three dimensions. One of the fascinating characteristics of SAQDs is their discrete density of states (DOS) with large energy-level spacing, in which acoustic phonon-mediated scattering should be suppressed compared with higher-dimensional structures. As a consequence, excitons in SAQDs are expected to exhibit long coherence time, which is advantageous for application of quantum information processing. In terms of inter-level relaxation, interaction with longitudinal optical (LO) phonons is an important aspect of SAQDs. These phonon-mediated transitions can be confirmed in the single-dot photoluminescence excitation (PLE) spectra, in which the reduction of relaxation paths renders individual LO phonons visible in the ground state emissions. To date several LO phonon-related transitions including bulk GaAs have been clearly observed. In the energy region higher than … More 1LO, single-dot PLE spectra reveal a number of intense PLE features, recognized as 2LO phonon resonances. As excitonic excited states are also present, several relaxation pathways with qualitatively different processes exist in the 2LO region.In this research, we investigate in detail the 2LO resonances in the single-dot PLE. Several 2LO resonances emerge as dip structures in the peaks under various conditions of excitation power. The observed dip structures suggest line broadening, even in the individual resonace lines. In contrast, the corresponding biexciton resonances still have sharp peaks, indicating that the 2LO resonances consist of several relaxation channels with differing scattering processes. These observations can explain why PLE resonances exhibit short dephasing times even in single SAQDs. Moreover, we found that phonon mediated transitions can be largely removed by two-color excited PLE spectroscopy. The reduction of line broadening indicates that the PLE includes a number of phonon-related transitions with large relaxation windows. Less