In recent years, there has been a fascinating exchange of ideas between the seemingly disparate fields of condensed matter physics, quantum computer science and quantum gravity. Each has contributed profoundly to our current understanding of the real time dynamics of generic many body systems with local Hamiltonians. A key element to these connections has been a deeper understanding of the entanglement pattern which exists and persists in many body wavefunctions at strong coupling. By tracking the growth of entanglement under unitary evolution starting from simple, atypical states, one can concretely address questions relating to the onset of thermalisation and the validity of hydrodynamics as a valid description at long distances. At this point, it's useful to distinguish between systems which are integrable and systems which are chaotic since the growth of entanglement qualitatively differs in both settings. Remarkably though, these 2 behaviours are thought to be entirely universal, in the sense that, the manner in which quantum information gets delocalised appears to share the same characteristics in all chaotic systems and likewise in all integrable systems. Inspired by this apparent universality, effective descriptions have been put forward which attempt to provide simple explanations for the growth of entanglement in either case. For integrable systems, this is the famous "quasi-particle spreading picture" put forth by Cardy and Calabrese whereas, for chaotic systems, the effective description is the so called “membrane picture” of Nahum et al. The purpose of this talk will be to explain all of this in greater detail with the aid of simple models and to tie some loose threads in the literature.
