Abstract

Light cannot be focused to better than half its wavelength; the well-known diffraction limit thus prevents spatially resolved spectroscopy of individual nanostructures and their ultrafast dynamic processes. This talk will show how we can circumvent that limit and gain access to the nanometer spatial scale on a femtosecond time scale using coherent control concepts [Nature 446, 301 (2007); PNAS 107, 5329 (2010)]. Recently, we have combined this approach with coherent two-dimensional spectroscopy. Thus we were able to realize four-wave mixing experiments with 50 nm spatial resolution [Science, 11 August 2011 (10.1126/science.1209206)]. Unexpected long electronic phase coherences in metal nanostructures were observed and explained. Applications are envisaged for nonlinear spectroscopy of nanostructures, molecular aggregates or “artificial molecules” on surfaces, nanophotonic circuits, photovoltaic devices, coupled quantum dots, and others. It should thus become possible in the future to study a broad range of fascinating quantum phenomena with direct space–time resolution.