Calendar of Physics Talks Vienna

Stable, ghost-free solutions in UV non-local gravity
Speaker:Shubham Maheshwari (Groningen U.)
Abstract:I consider higher derivative, UV modifications to GR. In particular, I will focus on a specific kind of string theory-inspired higher derivative gravity where one includes derivatives to all orders in the action. First, I will discuss how such a non-local theory of gravity admits stable, non-singular bouncing solutions in the absence of matter. Moreover, around this bouncing background, there exists only one propagating (and ghost-free) scalar mode, and no vector or tensor modes. Next, I will discuss the general analysis of scalar-vector-tensor perturbations in non-local gravity - in particular, I will show how non-local gravity is ghost-free around (A)dS and certain non-maximally symmetric backgrounds, and how certain (A)dS backgrounds have special physical spectra in that the propagating degrees of freedom are different from usual expectations.
Date: Thu, 22.10.2020
Time: 16:00
Duration: 60 min
Contact:Laura Donnay, Daniel Grumiller

Bartnik's quasi-local mass conjectures
Speaker:Lan-Hsuan Huang (University of Connecticut)
Abstract:Bartnik's quasi-local mass for a compact manifold with boundary is defined by minimizing the ADM masses among admissible extensions. Among several proposed conjectures, Bartnik's stationary conjecture asserts that a minimizing initial data set must be vacuum and admit a timelike Killing vector. We make partial progress toward this conjecture by showing that a minimizing initial data set must sit in a "null dust" spacetime carrying a global Killing vector. On the other hand, we find pp-wave counterexamples to Bartnik's stationary and strict positivity conjectures in dimensions greater than 8. In our proof, we introduce the concept of improvability of the dominant energy scalar, and we derive strong consequences of non-improvability using a new infinite-dimensional family of deformation to the Einstein constraint operator. This talk is based on a joint work with Dan Lee.
Date: Thu, 22.10.2020
Time: 16:00
Duration: 60 min
Contact:Piotr Chrusciel, David Fajman

Quantum Photonics
Speaker:Philip Walther (Universität Wien)
Abstract:The precise quantum control of single photons, together with the intrinsic advantage of being mobile make optical quantum system ideally suited for quantum information applications that require communication or the delegation of tasks. Prominent examples include quantum cryptography as well as quantum clouds and quantum computer networks. Here I present the current architectures for scalable photonic quantum computers and special purpose applications that exploit advantages of photonic quantum systems. In particular, I will present resent demonstrations of quantum-enhanced data security for quantum and classical computers. The latter is based on feasible hybrid classical-quantum technology, which shows promising new applications of readily available quantum photonics technology for complex data processing. By using tuneable integrated circuits I will also discuss the experimental realiz
Date: Fri, 23.10.2020
Time: 15:30
Duration: 45 min
Location:Hörsaal ATI
Contact:Jörg Schmiedmayer