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\newtheorem{prop}{Proposition} \newtheorem{cor}{Corollary} \newtheorem*{utheorem}{Theorem} \newtheorem*{ulemma}{Lemma} \newtheorem*{uprop}{Proposition} \newtheorem*{ucor}{Corollary} \theoremstyle{definition} \newtheorem{defn}{Definition} \newtheorem{example}{Example} \newtheorem*{udefn}{Definition} \newtheorem*{uexample}{Example} \theoremstyle{remark} \newtheorem{remark}{Remark} \newtheorem{note}{Note} \newtheorem*{uremark}{Remark} \newtheorem*{unote}{Note} %------------------------------------------------------------------- \begin{document} %------------------------------------------------------------------- \section*{holographic entanglement entropy} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{physics}{}\paragraph*{{Physics}}\label{physics} [[!include physicscontents]] \hypertarget{measure_and_probability_theory}{}\paragraph*{{Measure and probability theory}}\label{measure_and_probability_theory} [[!include measure theory - contents]] \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak \noindent\hyperlink{RyuTakayanagiFormula}{Ryu-Takayanagi formula}\dotfill \pageref*{RyuTakayanagiFormula} \linebreak \noindent\hyperlink{emergence_of_bulk_spacetime_from_boundary_information_theory}{Emergence of bulk spacetime from boundary information theory}\dotfill \pageref*{emergence_of_bulk_spacetime_from_boundary_information_theory} \linebreak \noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak \noindent\hyperlink{References}{References}\dotfill \pageref*{References} \linebreak \hypertarget{idea}{}\subsection*{{Idea}}\label{idea} Holographic entanglement entropy refers to the expression of [[entanglement entropy]] of [[quantum field theories]] expressed ``holographically'' via a version of [[AdS-CFT duality]] in terms of the [[geometry]] of a higher-dimensional [[bulk]] [[spacetime]] \hypertarget{RyuTakayanagiFormula}{}\subsubsection*{{Ryu-Takayanagi formula}}\label{RyuTakayanagiFormula} For [[quantum field theories]] that are exhibited as [[boundary field theories]] on the [[asymptotic boundary]] $A$ of an approximately [[anti de Sitter spacetime]] via some approximation to [[AdS-CFT duality]] (for instance for [[QCD]] via [[AdS-QCD duality]]) their [[entanglement entropy]] of a given [[bounded set|bounded domain]] $B\subset A$ turns out to be proportional to the [[area]] of the minimal-area [[surface]] inside the [[bulk]] spacetime that has the same [[boundary]] $\partial B$ (see \hyperlink{NishiokaRyuTakayanagi09}{Nishioka-Ryu-Takayanagi 09 (3.3)} for review of the formula and \hyperlink{LewkowyczMaldacena13}{Lewkowycz-Maldacena 13} for a conceptual explanation). \begin{quote}% graphics grabbed from \hyperlink{NishiokaRyuTakayanagi09}{Nishioka-Ryu-Takayanagi 09} \end{quote} This relation is known as the \emph{Ryu-Takayanagi formula} (\hyperlink{RyuTakayanagi06a}{Ryu-Takayanagi 06a}, \hyperlink{RyuTakayanagi06b}{Ryu-Takayanagi 06b}) for holographic computation of entanglement entropy, or \emph{holographic entanglement entropy}, for short. This is a generalization of the proportionality of [[black hole entropy]] to the area of its [[event horizon]]. Indeed, [[AdS-CFT duality]] applies to the [[near horizon geometry]] of [[black branes]], the higher-dimensional generalizations of [[black holes]] and reduces 4d black holes under suitable [[KK-compactification]] (see also at \emph{[[black holes in string theory]]}) \begin{quote}% graphics grabbed from \hyperlink{NishiokaRyuTakayanagi09}{Nishioka-Ryu-Takayanagi 09} \end{quote} In fact quantum corrections to the [[black hole entropy]] in the presence of matter fields is equal to the [[entanglement entropy]]. (\hyperlink{RyuTakayanagi06a}{Ryu-Takayanagi 06a, p. 13}) Various properties of [[entanglement entropy]] find immediate geometric interpretations this way, for instance subadditivity \begin{quote}% graphics grabbed from \hyperlink{NishiokaRyuTakayanagi09}{Nishioka-Ryu-Takayanagi 09} \end{quote} \hypertarget{emergence_of_bulk_spacetime_from_boundary_information_theory}{}\subsubsection*{{Emergence of bulk spacetime from boundary information theory}}\label{emergence_of_bulk_spacetime_from_boundary_information_theory} Further discussion of implications of the Ryu-Takayanagi formula in \hyperlink{vanRaamsdonk10}{van Raamsdonk 10} suggested that the logic may also be turned around: Instead of computing [[entanglement entropy]] of a given [[boundary field theory]] from known [[bulk]] [[geometry]], conversely the [[bulk]] [[spacetime]] may be reconstructed from knowledge of the [[entanglement entropy]] of a boundary field theory. Talking this perspective to the extreme suggests a description of [[bulk]] [[spacetimes]] entirely in terms of [[information theory]]/[[entanglement]]-relations of a boundary [[QFT]] (``[[tensor networks]]'', \hyperlink{Swingle09}{Swingle 09}, \hyperlink{Swingle12}{Swingle 12}, and quantum error correction codes \hyperlink{ADH14}{ADH 14}, \hyperlink{PYHP15}{PYHP 15}, see \hyperlink{Harlow18}{Harlow 18} for review). \begin{quote}% graphics grabbed from \hyperlink{Harlow18}{Harlow 18} \end{quote} \begin{quote}% graphics grabbed from \hyperlink{Harlow18}{Harlow 18} \end{quote} In this context the Ryu-Takayanagi formula for holographic entanglement entropy (\hyperlink{RyuTakayanagiFormula}{above}) has an exact proof \hyperlink{PYHP15}{PYHP 15, Theorem 2}. \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item gravitational entropy \begin{itemize}% \item [[Bekenstein-Hawking entropy]] \item [[generalized second law of thermodynamics]] \item [[black holes in string theory]] \end{itemize} \item [[p-adic AdS-CFT]] \end{itemize} \hypertarget{References}{}\subsection*{{References}}\label{References} The original article are \begin{itemize}% \item [[Shinsei Ryu]], [[Tadashi Takayanagi]], \emph{Holographic Derivation of Entanglement Entropy from AdS/CFT}, Phys. Rev. Lett. 96:181602, 2006 (\href{https://arxiv.org/abs/hep-th/0603001}{arXiv:hep-th/0603001}) \item [[Shinsei Ryu]], [[Tadashi Takayanagi]], \emph{Aspects of Holographic Entanglement Entropy}, JHEP 0608:045, 2006 (\href{https://arxiv.org/abs/hep-th/0605073}{arXiv:hep-th/0605073}) \end{itemize} A proposal for a conceptual explanation is made in \begin{itemize}% \item Aitor Lewkowycz, [[Juan Maldacena]], \emph{Generalized gravitational entropy}, J. High Energ. Phys. (2013) 2013: 90 (\href{https://arxiv.org/abs/1304.4926}{arXiv:1304.4926}) \end{itemize} Review is in \begin{itemize}% \item Tatsuma Nishioka, [[Shinsei Ryu]], [[Tadashi Takayanagi]], \emph{Holographic Entanglement Entropy: An Overview}, J.Phys.A42:504008,2009 (\href{https://arxiv.org/abs/0905.0932}{arXiv:0905.0932}) \item Matthew Headrick, \emph{Lectures on entanglement entropy in field theory and holography} (\href{https://arxiv.org/abs/1907.08126}{arXiv:1907.08126}) \end{itemize} Survey talks include \begin{itemize}% \item Meyers, \emph{Holographic entanglement entropy}, (\href{http://www.lpt.ens.fr/IMG/pdf/Myers.pdf}{pdf slides}) \item Shinsei Ryu, \emph{Holographic geometry in Entanglement Renormalization} (\href{http://icmt.illinois.edu/Workshops/JointWorkshopPerimeter/Ryu-PI-ICMT-2012.pdf}{pdf slides}) \item Juan Jottar, \emph{(Entanglement) Entropy in three-dimensional higher spin theories} (\href{http://www.hip.fi/holograv13/talk_folder/Jottar-HologravWorkshop-March2013.pdf}{pdf slides}) \item Matthew Headrick, \emph{Entanglement entropies in holographic field theory} (\href{http://www.ggi.fi.infn.it/talks/talk1853.pdf}{pdf slides}) \item Tadashi Takayanagi, \emph{Entanglement Entropy and Holography (Introductory review)} (\href{http://www.princeton.edu/~jmaciejk/entanglement2012/slides/TakayanagiPCTS2012.pdf}{pdf slides}) \item Tom Hartmann, \emph{Entanglement entropy and geometry}, talk slides, 2014 (\href{http://online.kitp.ucsb.edu/online/qft14/hartman/pdf/Hartman_QFT14_KITP.pdf}{pdf}) \end{itemize} An influential argument that this relation implies that [[entanglement]] in the boundary theory is what makes spacetime as such appear in the bulk theory is due to \begin{itemize}% \item [[Mark Van Raamsdonk]], \emph{Building up spacetime with quantum entanglement}, Gen.Rel.Grav.42:2323-2329,2010; Int.J.Mod.Phys.D19:2429-2435,2010 (\href{https://arxiv.org/abs/1005.3035}{arXiv:1005.3035}) \item [[Mark Van Raamsdonk]], \emph{Building up spacetime with quantum entanglement II: It from BC-bit} (\href{https://arxiv.org/abs/1809.01197}{arXiv:1809.01197}) \end{itemize} reviewed in \begin{itemize}% \item [[Mark Van Raamsdonk]], \emph{Lectures on Gravity and Entanglement}, chapter 5 in New Frontiers in Fields and Strings TASI 2015 Proceedings of the 2015 Theoretical Advanced Study Institute in Elementary Particle Physics 2015 Theoretical Advanced Study Institute in Elementary Particle Physics (\href{https://arxiv.org/abs/1609.00026}{arXiv:1609.00026}) \end{itemize} Relation to [[renormalization]] of [[entanglement]] and [[tensor networks]] is due to \begin{itemize}% \item Brian Swingle, \emph{Entanglement Renormalization and Holography} (\href{https://arxiv.org/abs/0905.1317}{arXiv:0905.1317}) \item Brian Swingle, \emph{Constructing holographic spacetimes using entanglement renormalization} (\href{https://arxiv.org/abs/1209.3304}{arXiv:1209.3304}) \end{itemize} and further in terms of quantum error correcting codes due to \begin{itemize}% \item [[Ahmed Almheiri]], Xi Dong, [[Daniel Harlow]], \emph{Bulk Locality and Quantum Error Correction in AdS/CFT}, JHEP 1504:163,2015 (\href{https://arxiv.org/abs/1411.7041}{arXiv:1411.7041}) \item Fernando Pastawski, Beni Yoshida, [[Daniel Harlow]], John Preskill, \emph{Holographic quantum error-correcting codes: Toy models for the bulk/boundary correspondence}, JHEP 06 (2015) 149 (\href{https://arxiv.org/abs/1503.06237}{arXiv:1503.06237}) \end{itemize} reviewed in \begin{itemize}% \item [[Daniel Harlow]], \emph{TASI Lectures on the Emergence of Bulk Physics in AdS/CFT} (\href{https://arxiv.org/abs/1802.01040}{arXiv:1802.01040}) \end{itemize} See also \begin{itemize}% \item Felix M. Haehl, Eric Mintun, Jason Pollack, Antony J. Speranza, [[Mark Van Raamsdonk]], \emph{Nonlocal multi-trace sources and bulk entanglement in holographic conformal field theories}, J. High Energ. Phys. (2019) 2019: 005 (\href{https://arxiv.org/abs/1904.01584}{arxiv:1904.01584}, \href{https://youtu.be/kRCwzyliJ1M}{talk recording}) \end{itemize} Further development of these tensor networks in \begin{itemize}% \item Ning Bao, Geoffrey Penington, Jonathan Sorce, Aron C. Wall, \emph{Beyond Toy Models: Distilling Tensor Networks in Full AdS/CFT} (\href{https://arxiv.org/abs/1812.01171}{arXiv:1812.01171}) \item Ning Bao, Geoffrey Penington, Jonathan Sorce, Aron C. Wall, \emph{Holographic Tensor Networks in Full AdS/CFT} (\href{https://arxiv.org/abs/1902.10157}{arXiv:1902.10157}) \end{itemize} Computation of [[black hole entropy]] in 4d via [[AdS4-CFT3 duality]] from [[holographic entanglement entropy]] in the [[ABJM theory]] for the [[M2-brane]] is discussed in \begin{itemize}% \item Jun Nian, Xinyu Zhang, \emph{Entanglement Entropy of ABJM Theory and Entropy of Topological Black Hole} (\href{https://arxiv.org/abs/1705.01896}{arXiv:1705.01896}) \end{itemize} Discussion in terms of [[DHR superselection theory]]: \begin{itemize}% \item Horacio Casini, Marina Huerta, Javier M. Magan, Diego Pontello, \emph{Entanglement entropy and superselection sectors I. Global symmetries} (\href{https://arxiv.org/abs/1905.10487}{arXiv:1905.10487}) \end{itemize} [[!redirects Ryu-Takayanagi formula]] \end{document}