Attosecond Science and “spooky action at a distance”
Attosecond pulses that are generated by means of High‐Harmonic Generation have photon energies in the extreme ultra‐violet (XUV) or soft X‐ray regime, and are thus ionizing radiation. Consequently, the initial (“pump”) step in many attosecond pump‐probe experiments is an ionization step that converts a neutral atom or molecule into an ion and its accompanying photoelectron. It is often tempting to consider the outcome of the subsequent “probe” step in terms of the interaction of the probe laser with the ion or the photoelectron only, depending on whether we are interested in attosecond dynamics in the ion (e.g. charge migration) or in the photoelectron (e.g. streaking). However, the ion and the photoelectron are an entangled system, and this can have measurable consequences. In my talk I will discuss experimental and numerical work addressing the role of ion‐photoelectron entanglement in attosecond pump‐probe experiments and I will provide an update on these and other topics that we are currently investigating in our attosecond program at the Max‐Born Institute.