Correlation effects in high harmonic generation

Abstract

The generation of high harmonics (HHG) is the fundamental process that gave rise to attosecond physics. In the present thesis, we investigate this highly nonlinear process in large atomic systems with the aim of investigating correlation effects that have been neglected so far. For this purpose it is necessary to solve the time-dependent multi-electron Schrödinger equation, which, however, is plagued by its numerically unfavorable exponential scaling with the number of electrons. To overcome this bottleneck, we use the time-dependent two-particle reduced-density matrix (TD2RDM) method, which we benchmark against accurate wave-function based methods for small atoms. Using the TD2RDM we can push the system size from small atoms like beryllium and neon towards heavier atoms like argon or even xenon. Finally, we probe correlation effects during HHG in atoms employing correlation and entanglement measures known form quantum information theory.