Entropy transport in closed quantum many-body systems far from equilibrium

Abstract: We investigate entropy transport for universal scaling phenomena in closed quantum many-body systems far from equilibrium. From spatially resolved experimental data of a spinor Bose gas, we demonstrate that entropy decreases on long-distance scales while it increases at short distances. A dynamical separation of scales leads to macrophysics with long-range order, which is insensitive to the highly entropic microphysical processes. Since the total von Neumann entropy is conserved on a fundamental level for the quantum system, our analysis reveals a reciprocal connection between the emergence of macroscopic structure and microscopic disorder. To illustrate the scope of this connection, we exemplify the universal phenomenon also in a relativistic quantum field theory calculation from first principles, which is relevant for particle physics and early-universe cosmology.