This workshop will bring together experts working on complexity and related ideas in holography, quantum field theory, and quantum information theory. The workshop is hosted by the Gravity, Quantum Fields and Information group and will take place at the AEI in Potsdam from Monday, February 26th to Friday, March 2nd, 2018. The schedule of talks is below; ample time has been allotted for informal discussions, collaboration, and work. We look forward to welcoming you for a stimulating week!

## Monday 26.02

### 14:00 - 15:00 : Julian Sonner (joint AEI seminar)

Titile: *Black Holes as Pure States*

Abstract: We would like to understand in detail how bulk quantum gravity arises from suitable boundary CFT. In recent years, remarkable progress has been made in this direction, in particular in three dimensions. An object of central interest in this story is the Virasoro identity block, and I will review how gravitational physics arises from this construction. I will pay particular attention to far-from equilibrium physics, which corresponds to the formation and eventual evaporation of black holes in the bulk. If time permits I will also comment on more general aspects of thermal physics in low dimensional holography, and in particular the role played by the eigenstate thermalization hypothesis (ETH).

### 15:00 : coffee break

## Tuesday 27.02

### 9:30 - 10:30 : Ben Craps

Title: *Entwinement*

Abstract: We develop the notion of entwinement to characterize the amount of quantum entanglement between internal, discretely gauged degrees of freedom in a quantum field theory. This concept originated in the program of reconstructing spacetime from entanglement in holographic duality. In this talk, we discuss two formal definitions of entwinement.

**10:30 & 15:30 : coffee break**

### 16:00 - 17:00 : Mohsen Alishahina

Title: *Holographic Complexity and Fidelity*

Abstract: In the context of CV complexity for a field theory with a gravitational dual, we study holographic fidelity susceptibility for two states related by a deformation of a relevant operator. Then using CA proposal of complexity we will further explore different aspects of holographic complexity.

## Wednesday 28.02

### 9:30 - 10:30 : Martin Ammon

Title: *Holographic Phonons*

Abstract: In the last decade the gauge/gravity duality has proven to be an efficient tool to tackle condensed matter questions in the context of strongly coupled physics. Despite the various directions and applications pursued, a fundamental piece of the condensed matter phenomenology is still missing in the holographic puzzle: a concrete, simple and clear realization of phonons. In the talk I present a class of holographic massive gravity models realizing spontaneous and/or explicit breaking of translational symmetry. In the case of spontaneous breaking, the models exhibit transverse phonon modes whose speed relates to the elastic shear modulus according to elasticity theory. Massive gravity theories thus emerge as versatile and convenient theories to model generic types of translational symmetry breaking: explicit, spontaneous and a mixture of both. The nature of the breaking is encoded in the radial dependence of the graviton mass. As an application of the model, I will compute the temperature dependence of the shear modulus and find that it features a glass-like melting transition.

**10:30 & 15:30 : coffee break**

### 16:00 - 17:00 : Jose Barbon

Title: *Terminal Holographic Complexity*Abstract: We introduce a notion of quasi-local action complexity, adapted to space times with space like singularities. We study its monotonicity properties in some exactly solvable examples. Furthermore, we discuss the conditions for the singularity to actually contribute to the complexity under coarse-graining.

## Thursday 01.03

### 9:30 - 10:30 : Michael Smolkin

Title: *On Entanglement and Quantum Quenches in CFT*

Abstract: I will report on recent progress in quantum quenches and discuss entanglement in this context.

**10:30 & 15:30 : coffee break**

### 16:00 - 17:00 : Alan Reynolds

Title: *Complexity of the AdS Soliton*

Abstract: We examine the holographic complexity conjectures as applied to the AdS soliton and its holographic dual, the ground state of a field theory on a torus with antiperiodic boundary conditions on one cycle, and we find striking qualitative differences between the complexity-volume (CV) and the complexity-action (CA) results. These results are compared to a simple field theory calculation for free fermions on a lattice.

## Friday 02.03

### 9:30 - 10:30 : Pawel Caputa

Title: *Complexity of Path Integrals in 2d Field Theories*

Abstract: I will talk about recent and ongoing works on defining complexity from optimization of path integrals in 2 dimensional field theories.

### 10:30 : coffee break

### Practical information:

Invited participants will be housed in the on-campus guesthouse, the keys for which may be picked up upon arrival at the reception desk in the central building. The reservation and payment will be taken care of on our end; you don't need to do anything. Additionally, all participants will receive a desk at the institute, and wifi is available throughout the campus.

The easiest way to reach the AEI is by taking one of the trains from Berlin to Golm, from which the institute is a short 5-10 minute walk. Note that depending on the time of day, it may be necessary to change trains in Potsdam Hbf. There are frequent trains between Potsdam and Golm, in addition to a (slower but more frequent) bus service (lines 605 & 606) that stops directly at the campus. More details, including a map of the Max Planck campus, can be found here.

Breakfast and lunch will be available in the on-campus cafeteria, located in the central building. For dinner, there are a wide variety of restaurants in Potsdam. Additionally, there is a REWE supermarket just across the train tracks from the guesthouse, and the latter is equipped with a kitchen if you wish to prepare some basic meals yourself.

If you have further questions, please do not hesitate to contact the organizer.