Entropy from Entanglement

The usual picture of entropy in statistical mechanics is that it quantifies our degree of ignorance about a system. Recent advances in cooling and trapping atoms allow the preparation of quantum systems with many interacting particles isolated from any external environment. Textbook discussions of entropy — that invoke the presence of a “large” environment that brings the system to thermal equilibrium at a fixed temperature --- cannot apply to such systems. Sid Parameswaran will explain how “entropy” of subsystems of such isolated quantum systems arises from quantum entanglement between different parts of the system, and how their approach to thermal equilibrium is best described as the `scrambling’ of quantum information as it is transferred to non-local degrees of freedom.