GENERAL PHYSICS COLLOQUIUM _____ Title: Attosecond science: shining new light on old questions in quantum mechanics Speaker: Ursula Keller, ETH Zürich, Physics Department, Zürich, Switzerland Time: Wednesday, 15 June, 2011 at 3:15 p.m. Place: Physics Auditorium, 3rd floor, Department of Physics Abstract Continued progress in novel light sources enables improved understanding of how matter functions, and how energy and charge are transported on an atomic scale. This research is necessary to further develop key basic physical understanding required to address important challenges such as alternative energy sources and improving health. Theoretical models often fail to describe the dynamics due to numerical limitations, and we need to develop better approximate models for the ultrafast dynamics on an atomic scale, where quantum mechanics becomes essential. Novel time-resolved attosecond streaking techniques such as energy streaking and the attoclock are currently being applied in an attempt to answer a very fundamental question in quantum mechanics: how fast can light remove a bound electron from an atom or a solid? For example two different techniques addressed two different fundamental processes: strong laser field ionization, where a the strong laser field bends the binding potential to emit an electron by tunnelling (tunnel ionization) and the photoelectric effect, where a single light quanta (a photon) is absorbed to emit an electron (photoemission). In the first case, an instantaneous tunnelling delay time in helium was measured within the experimental accuracy of around 10 as, and in the latter case, a relative delay in photoemission of about 20 as between electrons originating from different bound states in neon was measured - from a semi-classical point of view a somewhat puzzling outcome! Strong laser field ionization involves the absorption of many photons, and furthermore the electron emitted into the continuum (i.e. an unbound state) initially experiences a spatial separation from the ion of more than ten atomic units. For photoemission, in contrast, only one photon is absorbed without any initial lateral displacement. Why does photoemission, in contrast to tunnel ionization, have a measurable emission delay, we may wonder? As we know, quantum mechanics may give unexpected results as viewed from a classical perspective. Future results should hopefully help to resolve this potential controversy and give us a better physical picture to understand attosecond quantum mechanics. _____ Coffee/tea and cake will be served at 3 p.m. David Field