Attosecond Correlation Dynamics

Photoemission of an electron after a multi-electron system has absorbed a photon is commonly treated as one-particle phenomenon. Here we show how attosecond streaking spectroscopy in helium unveils the breakdown of this singleactive-electron approximation by recording up to 6 attoseconds retardation of the dislodged photoelectron due to the influence of electronic correlations. We measure the photon-energy-dependent emission timing of electrons liberated from the helium ground state by a ~100 eV photon, either leaving the ion in its ground state or exciting it into a shake-up state. The study identifies an optical field driven DC-Stark-shift of charge-asymmetric ionic states formed after the entangled photoemission as key contribution to the observed correlation time shift and provides means towards complete wavepacket reconstruction. The sub-attosecond agreement with the predictions of quantum mechanical abinitio modelling allows to determine the absolute zero of time in the photoelectric effect to a precision better than 1 25 ⁄ –th of the atomic unit of time.