Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 354 2 b ii Solution Created 2026-09-24 Updated 2026-09-25
There are two competing extremal-surface topologies. The disconnected candidate has area independent of the separation and gives . A connected surface joining the two boundary circles can have smaller area when the gap is small; as , short-distance entanglement across the nearby boundaries makes positive and divergent.
Increasing makes the connected candidate less favorable. At a critical separation its area equals the disconnected area, and beyond that point the disconnected candidate is minimal. This entanglement-wedge phase transition gives