InaRIS Fellow (2020-2029)

Tadashi Takayanagi

Professor,Yukawa Institute for Theoretical Physics, Kyoto University*Profile is at the time of the award.

2020InaRISScience & Engineering

Research topics
Emergence of quantum gravity from quantum entanglement
The Ryu-Takayanagi formula, an equation derived by Dr. Takayanagi and Dr. Ryu, is gaining recognition as it could lead to the elucidation of the quantum gravity theory, a physical principle of gravity at the micro-level. This formula explains how entanglement entropy, a measure how much a given quantum state is quantum mechanically entangled is related to the geometry of the universes, and suggests that the universe described by quantum gravity theory could emerge from quantum information. The purpose of his research is to advance this uniquely creative idea further to elucidate the quantum gravity theory, in quest of the origin of the universe at the micro-level.



One of the primary concerns of theoretical physics is to gain complete understanding of the physical principles of gravity at micro-level, that is, to elucidate the quantum gravity theory. A holographic derivation of entanglement entropy published in 2006 by Dr. Tadashi Takayanagi and Dr. Shinsei Ryu (Ryu–Takayanagi formula) has been one of the most important breakthrough discoveries since Dr. Juan Maldacena proposed AdS/CFT (anti-de-Sitter/conformal field theory) correspondence in 1997. So significant was their derivation that it changed the whole surface of the research trends in this field. In an interview conducted after receiving the 2014 Kyoto Prize, Dr. Edward Witten cited the Ryu–Takayanagi formula as the first on the list of “highlights in the past fourteen years.” Owing to its microscopic explanations based on AdS/CFT correspondence, the Ryu–Takayanagi formula has secured a critical position in theoretical physics.
For 14 years since announcing it, Dr. Takayanagi has continuously evolved the Ryu–Takayanagi formula to make leading contributions to the theoretical elucidation of the holographic principle and its application. Dr. Takayanagi and Dr. Matthew Headrick, for example, discovered that a strongly subadditive inequality of von Neumann entropy corresponds to a triangle inequality of the minimum surface, a geometric characteristic of the Ryu–Takayanagi formula. Revealing that the profound nature of entropy is reflected in a geometric structure of gravity theory, this discovery has significantly catalyzed the subsequent development in this field. Furthermore, over the past several years, it has become clear that quantum error correction codes of the quantum information theory are playing important roles in the microscopic mechanism of the holographic principle. The Ryu–Takayanagi formula plays an essential role in the elucidation of this mechanism as well.
The research topic that Dr. Takayanagi has proposed aims to further advance the novel idea of a close relationship between “quantum information” and the “quantum gravity theory,” which has become widespread after the publication of the Ryu–Takayanagi formula, and to bring about a breakthrough in the elucidation of the quantum gravity theory, understanding of which is still in the early stages. Some of the relevant and recent research findings by Dr. Takayanagi include: “entanglement of purification” (an amount of entanglement entropy extended to its mixed state) is equal to the cross-section of a certain wormhole in AdS/CFT correspondence, and that, when calculating the path integral of the conformal field theory by discretizing it, geometric features of anti-de Sitter space (AdS) appear by themselves if the most efficient discretization process is required. It is expected that a new phase of research will be developed based on these findings.
The series of research efforts by Dr. Takayanagi, which have resulted in the discovery of an entanglement entropy formula in the holographic principle and its subsequent progress, have marked fundamental achievements in the quantum gravity theory and superstring theory. His research also facilitates collaboration between the condensed matter theory and quantum information theory. In addition to these impressive fruits of research, Dr. Takayanagi is an excellent academic advisor, under whose tutelage numerous young researchers have been produced. Dr. Takayanagi is a world-leading researcher of superstring theory and, with support from the InaRIS Fellowship Program, is expected to be a driving force for theoretical physics research in Japan over the next decade.

Message from fellow

I decided to apply to this fellowship because it offers such generous support for a full decade. Because I’m involved in basic research, I must hunker down and tackle a very challenging problem over time. It’s incredibly gratifying to have such extended support. With financial backing from the InaRIS Fellowship Program, I intend to address the fundamental topic of the origin of our universe.

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