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

TL;DR

This paper explores entropy transport in closed quantum many-body systems far from equilibrium, revealing a reciprocal relationship between macroscopic order and microscopic disorder through experimental and theoretical analysis.

Contribution

It demonstrates entropy decrease at long distances and increase at short distances in quantum systems, linking microphysical disorder to emergent macroscopic order.

Findings

Entropy decreases on long-distance scales.

Entropy increases at short distances.

Universal scaling phenomena observed in experiments and theory.

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.