Learning the Alpha-bits of black holes

• Published in: The journal of high energy physics Vol. 2019; no. 12; pp. 1 - 55
• Main Authors: Hayden, Patrick, Penington, Geoffrey
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.12.2019; Springer Nature B.V; SpringerOpen
• Subjects: AdS-CFT Correspondence; Black holes; Classical and Quantum Gravitation; Codes; Dependence; Elementary Particles; Error correction; Error correction & detection; Gauge-gravity correspondence; Hawking radiation; High energy physics; Lower bounds; Operators; Physics; Physics and Astronomy; Quantum entanglement; Quantum Field Theories; Quantum Field Theory; Quantum phenomena; Quantum Physics; Radiation; Reconstruction; Regular Article - Theoretical Physics; Relativity Theory; String Theory; Subspaces; Tensors; Wedges; AdS-CFT Correspondence; Gauge-gravity correspondence
• DOI: 10.1007/JHEP12(2019)007
• ISSN: 1029-8479

A bstract When the bulk geometry in AdS/CFT contains a black hole, boundary subregions may be sufficient to reconstruct certain bulk operators if and only if the black hole microstate is known, an example of state dependence. Reconstructions exist for any microstate, but no reconstruction works for all microstates. We refine this dichotomy, demonstrating that the same boundary operator can often be used for large subspaces of black hole microstates, corresponding to a constant fraction α of the black hole entropy. In the Schrödinger picture, the boundary subregion encodes the α -bits (a concept from quantum information) of a bulk region containing the black hole and bounded by extremal surfaces. These results have important consequences for the structure of AdS/CFT and for quantum information. Firstly, they imply that the bulk reconstruction is necessarily only approximate and allow us to place non-perturbative lower bounds on the error when doing so. Second, they provide a simple and tractable limit in which the entanglement wedge is state dependent, but in a highly controlled way. Although the state dependence of operators comes from ordinary quantum error correction, there are clear connections to the Papadodimas-Raju proposal for understanding operators behind black hole horizons. In tensor network toy models of AdS/CFT, we see how state dependence arises from the bulk operator being ‘pushed’ through the black hole itself. Finally, we show that black holes provide the first ‘explicit’ examples of capacity-achieving α -bit codes. Unintuitively, Hawking radiation always reveals the α -bits of a black hole as soon as possible. In an appendix, we apply a result from the quantum information literature to prove that entanglement wedge reconstruction can be made exact to all orders in 1 /N .