Real-time reconstruction of complex non-equilibrium quantum dynamics of matter

Abstract

Causality implies that by measuring an absorption spectrum, the time-dependent linear response function can be retrieved. Recent experiments suggest a link between the shape of spectral lines observed in absorption spectroscopy with the amplitude and phase of the systems response function. This has even been observed in the presence of strong, nonlinear interactions, which promote the observed system out of equilibrium, making it explicitly time dependent. Thus far, however, only the special case of a sudden modification of the response function was understood analytically, leaving the general case of the dynamical response to arbitrary interactions open to interpretation. Here, we demonstrate that even for the case of a strongly driven, time-dependent system, one can reconstruct the full temporal response information from a single spectrum if a sufficiently short signal is used to trigger the absorption process. This finding is directly applied to a time-domain observation of Rabi cycling between doubly-excited atomic states in the few-femtosecond regime. This general approach unlocks single-shot real-time-resolved signal reconstruction across time scales down to attoseconds for non-equilibrium states of matter. In contrast to available pump-probe schemes, there is no need for scanning time delays in order to access real-time information. The scientific applications of this technique range from testing fundamental quantum dynamics, to measuring and controlling ultrafast, chemical and biological reaction processes.