Utilizing a nanoantenna for ultrafast spectroscopy of a single semiconductor nanocrystal

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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.