Behind the Horizon in AdS/CFT

TL;DR

The paper tackles the problem of representing black hole interior operators in AdS/CFT, especially for mixed CFT states. It extends the Papadodimas–Raju approach by embedding the CFT in a quantum-error-correcting code with a code subspace and introducing Kraus-like interior operators and recovery mappings, enabling a linear mirror construction that satisfies a derived interior-exterior correspondence within the code. The interior operators act consistently with exterior mode algebras and entanglement, preserving a smooth horizon and challenging firewall scenarios within the code subspace, though limitations arise at high entropy. It also proposes incorporating an external system to achieve effectively linear, state-independent descriptions on the full Hilbert space, linking AdS/CFT interior reconstruction to quantum information concepts and clarifying the role of measurement in selecting semiclassical realities.

Abstract

We extend the recent proposal of Papadodimas and Raju of a CFT construction of operators inside the black hole interior to arbitrary non-maximally mixed states. Our construction builds on the general prescription given in earlier work, based on ideas from quantum error correction. We indicate how the CFT state dependence of the interior modes can be removed by introducing an external system, such as an observer, that is entangled with the CFT.