Observation of relaxation stages in out-of-equilibrium closed quantum systems
The temporal evolution of a non-equilibrium quantum system is the most crucial aspect of its dynamics. We introduce ro-translational excitations in an 87Rb Bose-Einstein condensate, which, under certain conditions, induces turbulence in the system . Once this non-equilibrium state is achieved, the system is allowed to evolve until it reaches equilibrium. Throughout this dynamical process, the characteristic particle cascade is observed, featured by the appearance of a power-law in the momentum distribution along with temporal windows of meta-stability showing the emergence of universal scaling. Subsequently, the system reaches a pre-thermalization stage with minimal variation, followed by a reverse cascade that forms a new condensate with fraction and temperature different from the initial one. This allows the assessment of various energy inputs during relaxation. The system is investigated under different initial excitations and represents a closed system suitable for exploring new physics related to the relaxation dynamics of non-equilibrium quantum systems.