Page Curve of average subsystem entropy

TL;DR

This paper analyzes the Page curve, describing how average subsystem entropy varies with subsystem size, and explores its implications for the black hole information paradox.

Contribution

It provides a detailed explanation of the Page curve's shape and its connection to quantum states and black hole information loss.

Findings

Subsystem entropy rises then falls with subsystem size.

The curve peaks when the subsystem is half the total system.

Connection established between the Page curve and black hole information paradox.

Abstract

The Page curve is a curve of average subsystem entropy as a function of subsystem size. The curve starts from 0, rises, peaks near the maximal possible entropy when the subsystem makes up half of the total system, and then falls back to 0. We here describe subsystem entropy, averaging over quantum states, and why the curve rises and falls in that manner. We also discuss the connection between the curve and the black hole information paradox.