Utilizing a nanoantenna for ultrafast spectroscopy of a single semiconductor nanocrystal

半导体纳米结构显示出迷人的光学性质。电子的强限制导致了大的量子化效应。胶体纳米晶在光伏、量子光学等领域有着广泛的应用。为了详细了解光物理，我们需要在单个纳米晶体水平上的光学光谱，否则系综平均将模糊许多方面。单一胶体的线性光谱是一种成熟的技术，但电荷分离的超快动力学只能通过非线性光谱来获得。然而，对于单一胶体，由于非线性效应的相互作用截面很小，超快光谱到目前为止是不可能完成的任务。在这里，我建议使用光学纳米天线来增强光与物质的相互作用。正如我们已经展示的单个金属纳米颗粒的瞬时吸收，一个简单的等离子体天线就可以将非线性响应提高10倍。在本项目中，我们想要建立在这个基础上。由于天线的增强，单纳米晶体的非线性光谱将首次成为可能。这将使我们能够在激发后不久研究电子动力学，它负责光伏中的电荷转移和量子比特中纳米晶体的相干操作。

Semiconductor nanostructures show fascinating optical properties. The strong confinement of the electrons leads to large quantization effects. Colloidal nanocrystals find applications in diverse fields such as photovoltaics and quantum optics. For a detailed understanding of the photophysics we need optical spectroscopy on the level of single nanocrystals, as otherwise the ensemble average will blur many aspects. Linear spectroscopy of a single colloid is a well established technique, but the ultrafast dynamics of charge separation can only be obtained by nonlinear spectroscopy. However, for a single colloid ultrafast spectroscopy is an impossible task up to date, due to the small interaction cross sections for nonlinear effects. Here, I propose to employ an optical nanoantenna to enhance the light-matter interaction. As we have shown for the transient absorption of a single metal nanoparticle, already a simple plasmonic antenna can enhance the nonlinear response by a factor of 10. In the present project we want to build on this. For the first time, nonlinear spectroscopy of single nanocrystal will become possible due to antenna enhancement. This will allow us to investigate electron dynamics shortly after excitation which is responsible for charge transfer in photovoltaics and the coherent operation of the nanocrystals in a quantum bit.