Coherent multidimensional spectroscopy of dilute gas-phase nanosystems

Two-dimensional electronic spectroscopy (2DES) is one of the most powerful spectroscopic techniques, capable of attaining a nearly complete picture of a quantum system including its couplings, quantum coherence properties and its real-time dynamics. While successfully applied to a variety of condensed phase samples, high precision experiments on isolated quantum systems in the gas phase have been so far precluded by insufficient sensitivity. However, such experiments are essential for a precise understanding of fundamental mechanisms and to avoid misinterpretations, e.g. as for the nature of quantum coherences in energy trans-port. Here, we solve this issue by extending 2DES to isolated nanosystems in the gas phase prepared by helium nanodroplet isolation in a molecular beam-type experiment. This approach uniquely provides high flexibility in synthesizing tailored, quantum state-selected model systems of single and many-body properties. For demonstration, we deduce a precise and conclusive picture of the ultrafast coherent dynamics in isolated high-spin Rb2 molecules and present for the first time a dynamics study of the system-bath interaction between a single molecule (here Rb3) and a superfluid helium environment. The results demonstrate the unique capacity to elucidate prototypical interactions and dynamics in tailored quantum systems and bridges the gap to experiments in ultracold quantum science.