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In this talk, I will present some of our recent research work on studying the collective photoexcitation dynamics of doped He nanodroplets - a superfluid quantum system which can be prepared in the laboratory by supersonic expansion (without the need for laser cooling). We will look at the dynamics in these nanodroplets under photoexcitation by two different photon sources: (i) intense few-cycle femtosecond (~10 fs) IR laser pulses and (ii) extreme ultraviolet (EUV) pulses from a synchrotron. In the case of IR pulse excitation, collective dynamics leads to a dynamic resonance which depends on plasmon morphology and can be understood in terms of a largely classical picture. Under EUV photoexcitation, however, the dynamics is dominated by quantum many-body effects. Here, we succeed in using "marker" atoms (dopants) placed in or on He nanodroplet to trace quantum dynamics. These studies strongly motivate and open-up new research avenues with few-fs (IR) and attosecond (EUV) pulses to interrogate these systems on timescales natural to the dynamics of electrons. |