Attosecond correlated electron dynamics

Electron-electron interactions, often called electron correlations, are well known to govern fundamental properties of matter, ranging from conductivity and magnetism to chemical bonds and chemical properties. Unlike those stationary properties, the role of electron correlations in dynamic processes on ultrafast time scales is still largely unexplored and has only recently become accessible. The natural time scale of electronic dynamics in atoms, molecules and solids is attoseconds which can now be explored by state-of-the art techniques involving few-cycle optical and XUV pulses. The goal of the present project is to theoretically investigate the influence of electron correlations on the timing of electron emission following the absorption of one or two photons. We will study how electron correlations affect the emission time by a full ab-initio simulation for helium and the hydrogen anion for which the two-electron dynamics can be solved numerically but exactly.

Electronic dynamical processes occur on the ultrafast time scale of attoseconds. With recent advances through the development of laser-based pump-probe interrogation techniques, time resolving attosecond electronic processes have become accessible. Investigation of the attosecond electronic processes serves an important role to verify the fundamental quantum mechanical laws and may lead to breakthroughs in the underlying physics on the level of the microscopic world. Together with other theoretical and experimental groups, we have studied the ultrafast electronic dynamics within a few prototypical scenarios, in particular with focus on electron correlations. One highlight of the present project is the conceptual development of a precision timing tool called the zeptosecond angular streak camera (ZASC). Compared to conventional tools that can access electronic processes down to the attosecond level, the ZASC improves the available state-of-the-art precision by two orders of magnitude, so that even faster dynamical processes on the zeptosecond level come into reach for the first time. With such unprecedented timing precision, a number of ultrafast dynamical processes that were previously hidden could be uncovered. Another highlight is the discovery of the interrelation between the energy and momentum exchange in light-matter interaction. Photons, which make up laser pulses, possess energy and momentum. When a light pulse interacts with matter, both energy and momentum exchange between the light and the matter will occur. We find that the exchanges of energy and momentum are interrelated with each other on the subcycle ultrafast time scale. These exchanges are strongly intertwined. In the absence of subcycle time resolution, such interconnection between the energy and momentum exchange remains hidden. This example underscores the importance of an ultrafast temporal resolution of accessible techniques.