Quantum Maxwell Demon at the Black Hole Horizon: Thermodynamics, Information, and the Equivalence Principle

TL;DR

This paper explores how a quantum Maxwell demon operating near a black hole horizon demonstrates the interplay of quantum information, thermodynamics, and spacetime causality, revealing horizon-induced information loss and the preservation of the equivalence principle.

Contribution

It models a quantum Maxwell demon crossing the black hole horizon, analyzing how horizon-induced information loss affects thermodynamics and causality, and clarifies the coexistence of these principles.

Findings

External demon experiences degraded measurement correlations.

Work extraction is reduced due to horizon-induced information loss.

Internal demon's protocol aligns with flat spacetime, preserving the equivalence principle.

Abstract

We analyze a quantum Maxwell demon operating a Szilard engine in free fall near a black hole horizon, where quantum information, thermodynamics, and spacetime causality intersect. The demon is modeled as a coherent two-level system, and the working substance is a single particle in a one-dimensional chamber crossing the event horizon. As the chamber crosses the horizon, the particle's Hilbert space splits into accessible and inaccessible sectors, leading to non-unitary reduced dynamics for an external demon due to tracing over interior degrees of freedom. We construct explicit measurement, expansion, and wall removal protocols for demons located outside or inside the horizon. Our results show that an external demon experiences degraded measurement correlations and reduced work extraction due to horizon-induced information loss, yet still obeys local thermodynamics and Landauer's principle. For an internal demon, the protocol reduces locally to the flat spacetime case, preserving the equivalence principle at the level of dynamics. While the equivalence principle holds dynamically, quantum information processing provides an operational signature of the horizon through reduced accessibility and irreversible open system behavior, clarifying how information, causality, and thermodynamics coexist in black-hole spacetimes.