Decay and recurrence of non-Gaussian correlations in a quantum many-body system

Starting from a strongly correlated state, with highly non-Gaussian correlations, a Gaussian state can emerge dynamically over time. Experiments with ultracold atoms show how the mixing between phase and density fluctuations plays the crucial role. Gaussian models provide an excellent effective description of many quantum many-body systems ranging from condensed-matter systems(1,2) all the way to neutron stars(3). Gaussian states are common at equilibrium when the interactions are weak. Recently it was proposed that they can also emerge dynamically from a non-Gaussian initial state evolving under non-interacting dynamics(4-11). Here we present the experimental observation of such a dynamical emergence of Gaussian correlations in a quantum many-body system. This non-equilibrium evolution is triggered by abruptly switching off the effective interaction between the observed collective degrees of freedom, while leaving the interactions between the microscopic constituents unchanged. Starting from highly non-Gaussian correlations, consistent with the sine-Gordon model(12), we observe a Gaussian state emerging over time as revealed by the decay of the fourth- and sixth-order connected correlations in the quantum field. A description of this dynamics requires a novel mechanism for the emergence of Gaussian correlations, which is relevant for a wide class of quantum many-body systems. In our closed system with non-interacting effective degrees of freedom, we do not expect full thermalization(13-19). This memory of the initial state is confirmed by observing recurrences(20) of non-Gaussian correlations.

Automated summary

The experimental observation of the dynamic emergence of Gaussian correlations in a quantum many-body system is presented, triggered by abruptly switching off the effective interaction between collective degrees of freedom. Initially non-Gaussian correlations are gradually replaced by a Gaussian state over time, and this dynamic process is significant for various quantum many-body systems.