Multi-particle bound state formation following a quantum quench to the one-dimensional Bose gas with attractive interactions

We consider quantum quenches from an ideal Bose condensate to the Lieb-Liniger model with arbitrary attractive interaction strength. We focus on the properties of the non-equilibrium steady state reached at late times after the quench. Using recently developed methods based on integrability, we obtain an exact description of the stationary state for a large number of bosons. A distinctive feature of this state is the presence of a hierarchy of multi-particle bound states. We determine the dependence of their densities on interaction strength and obtain an exact expression for the stationary value of the local pair correlation $g_2$. We discuss ramifications of our results for cold atom experiments.