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 attosecond pump-probe experiments on the hydrogen molecule, performed already a decade ago, as a first example of an experiment where ion-photoelectron entanglement contributed to influencing the measured electron localization (Sansone et al., 2010), and will present recent simulations illustrating the role of ion-photoelectron entanglement in the vibrational dynamics that can be induced in the hydrogen molecular ion upon ionization of neutral hydrogen by an attosecond pulse.
Sansone, G., Kelkensberg, F., Perez-Torres, J. F., Morales, F., Kling, M. F., Siu, W., . . . Vrakking, M. J. J. (2010). Electron localization following attosecond molecular photoionization. Nature, 465(7299), 763-U763. doi:Doi 10.1038/Nature09084