Editorial

Abstract

Since the discovery of the AdS/CFT correspondence in 1997, this subject is one of the most interesting research topics in theoretical physics. The AdS/CFT correspondence, which holographically relates a gravitational theory in an anti-de Sitter bulk space to a conformally field theory on the AdS boundary, has led to many deep and new insights about the structure of gauge theories and about questions in quantum gravity and black holes. Furthermore the AdS/CFT correspondence was successfully applied to a broad range of concrete problems in strongly interacting systems, such as for the quark gluon plasma and in condensed matter physics. Several articles in “Fortschritte der Physik” were reporting on new developments within this field over the last years. Recently the concept of holographic entanglement has shed new light about the relation between gravity and gauge theories. Using the AdS/CFT correspondence it was possible to compute the entanglement entropy in a d-dimensional conformal quantum theory in terms of a minimal surface in the corresponding d+1 dimensional bulk geometry. This holographic derivation of entanglement entropy is reminiscent of the black hole entropy given in terms of the area of the event horizon. Holographic entanglement intertwines concepts in quantum information, such as entanglement, with concepts in general relativity and geometry. This intertwining between entanglement and geometry has also appeared in an article of J. Maldacena and L. Susskind (Fort.Phys. 61 (2013) 781), who give an interpretation of entanglement in quantum mechanics in terms of an Einstein-Rosen bridge between two black holes that form an EPR pair. Furthermore black holes can be view as kind of quantum computers, a picture, which recently also emerged in the context of a corpuscular description of black holes, being a Bose-Einstein condensate of gravitons. We expect that the field of holographic entanglement and the interrelation between quantum information and general relativity will further evolve during the next years and will give further new insights into the quantum nature of gravity. This edition of “Fortschritte der Physik” is devoted to recent papers on holographic entanglement, entanglement entropy, quantum measurement, black holes, cosmology and also about applications of holographic entanglement in condensed matter systems. We are glad and grateful that some of the leading scientists in this exciting field of research are contributing to the first edition of “Fortschritte der Physik” in 2016. We wish all authors and readers of “Fortschritte der Physik” a happy and successful new year 2016.