Attosecond real-time observation of electron tunnelling and multi-electron dynamics in atoms

This report presents the first real-time observation of electron tunnelling and multi-electron dynamics in atoms exposed to intense light. The observed sub-femtosecond ionization steps provide a powerful means of probing the transient population of short-lived valence electronic states in excited atoms offering direct, time-domain access to a wide range of multi-electron dynamics unfolding on an attosecond to femtosecond time scale. The results of pump-probe measurements are in good agreement with the predictions of the theory Keldysh put forward four decades ago.