  Turbulence is an intriguing non-equilibrium state, which originates from
fluid mechanics and has far-reaching consequences in the description of climate
physics, the characterization of quantum hydrodynamics, and the understanding
of cosmic evolution. The concept of turbulent cascade describing the energy
redistribution across different length scales offers one profound route to
reconcile fundamental conservative forces with observational energy
non-conservation of accelerating expansion of the universe bypassing the
cosmological constant. Here, we observe a dimension crossing turbulent energy
cascade in an atomic Bose-Einstein condensate confined in a two-dimensional
(2d) optical lattice forming a 2d array of tubes, which exhibits universal
behaviors in the dynamical energy-redistribution across different dimensions.
By exciting atoms into the optical-lattice high bands, the excessive energy of
this quantum many-body system is found to cascade from the transverse
two-dimensional lattice directions to the continuous dimension, giving rise to
a one-dimensional turbulent energy cascade, which is in general challenging to
reach due to integrability. We expect this observed novel phenomenon of
dimension-crossing energy cascade may inspire microscopic theories for modeling
positive cosmological constant of our inflationary universe.
