  We study the non-equilibrium dynamics of a one-dimensional Bose gas with
long-range interactions that decay as $(\frac{1}{r^{\alpha}})$ $(0.5 < \alpha
<4.0$). We investigate the system when the interactions are suddenly switched
from the Tonks-Girardeau (TG) to the super-Tonks-Girardeau (sTG) limit. We find
that relaxation is achieved through a complex intermediate dynamics
demonstrated by violent fragmentation and chaotic delocalization. We establish
that the sTG gas exhibits classical gaseous characteristics and an asymptotic
state associated with unbounded entropy production. The phase diagram shows an
exponential boundary between the nonthermal (quantum) gas and the thermal
(classical) gas. We show the universality of the dynamics by also presenting
results for spinless fermions. Weaker quench protocols give a certain degree of
control over the relaxation process and induce some intermediate
quasi-prethermal states. Our study showcases the complex relaxation behavior of
tunable long-range interacting systems that could be engineered in
state-of-the-art experiments, e.g. in trapped ions or Rydberg atoms.
