Qiss

Existence of processes violating causal inequalities on time-delocalised subsystems

Papers QISS1 / By

It has been shown that it is theoretically possible for there to exist quantum and classical processes in which the operations performed by separate parties do not occur in a well-defined causal order. A central question is whether and how such processes can be realised in practice. In order to provide a rigorous argument for the notion that certain such processes have a realisation in standard quantum theory, the concept of time-delocalised quantum subsystem has been introduced. In this paper, we show that realisations on time-delocalised subsystems exist for all unitary extensions of tripartite processes. Remarkably, this class contains processes that violate causal inequalities, i.e., that can generate correlations that witness the incompatibility with definite causal order in a device-independent manner. We consider a known striking example of such a tripartite classical process that has a unitary extension, and study its realisation on time-delocalised subsystems. We then discuss the question of what a violation of causal inequalities implies in this setting, and argue that it is indeed a meaningful concept to show the absence of a definite causal order between the variables of interest.

Poster for Don Marolf's virtual seminar: Spacetime wormholes, superselection sectors, and ensembles in quantum gravity: An Overview

Don Marolf
University of California Santa Barbara Spacetime wormholes, superselection sectors, and ensembles in quantum gravity: An Overview

Virtual Seminars / By

Don Marolf will review and summarize recent developments regarding spacetime wormholes in the gravitational path integral and their implications for the existence of a certain notion of “superselection sectors” in quantum gravity.  The existence of such sectors implies that, in certain contexts, we can think of quantum gravity as describing a statistical ensemble of theories.  …

Don Marolf
University of California Santa Barbara Spacetime wormholes, superselection sectors, and ensembles in quantum gravity: An Overview Read More »

Chris Smeenk Joins QISS. Expanded Visiting Philosophers Program.

News & Blog / By

We are happy to welcome Chris Smeenk to the consortium. Chris is the director of the Rotman Institute of Philosophy and professor of philosophy at Western University. In partnership with the Rotman Institute of Philosophy the current QISS visiting program aimed at philosophers will be significantly expanded, with the aim to train a new generation of philosophers of …

Chris Smeenk Joins QISS. Expanded Visiting Philosophers Program. Read More »

Richard Howl
Oxford UniversityTesting quantum gravity with non-Gaussianity and a Bose-Einstein condensate

Virtual Seminars / By

Due to rapid progress in experimental quantum information science, a table-top test of quantum gravity may soon be possible. A promising possibility is to place two micro-solids in a spatial superposition and separable state. If, after a short time, entanglement between the micro-solids is observed then this could provide evidence of a quantum theory of gravity, assuming all other interactions can be neglected and that gravity provides a local interaction. These proposals have raised a number of questions, such as whether entanglement generation would really provide a test of quantum gravity and whether the experiments are feasible in the near term. Here, we consider whether an alternative signature of quantum gravity to entanglement could be used for a table-top test, and an alternative experimental setting. Specifically, we consider non-Gaussianity rather than entanglement and how this could be searched for in a Bose-Einstein condensate (BEC) to evidence quantum gravity. We discuss whether using non-Gaussianity and a BEC could provide any advantages to entanglement and micro-solids.

Laurent Freidel
Perimeter InstituteThe nature of quantum entanglement in gravity: a tale about Noether and subsystems

Virtual Seminars / By

In this talk, I will present a new perspective about decomposing gravitational systems into subsystems. I will explain what is the nature of entanglement of gravitational subsystems and the importance of local symmetries. I will emphasize the central role of the corner symmetry group in capturing all the necessary data needed to glue back seamlessly quantum spacetime regions. I will explain some of the key results we have achieved in the construction of the representations of these groups. If time permits, I will present new results about the canonical description of open gravitational systems and what it teaches us about the nature of quantum gravitational radiation.

Emily Adlam
Western University, Rotman Institute of Philosophy Contextuality, Fine-tuning and Teleological Explanation

Virtual Seminars / By

In this talk I will assess various proposals for the source of the intuition that there is something problematic about contextuality, and argue that contextuality is best thought of in terms of fine-tuning. I will suggest that as with other fine-tuning problems in quantum mechanics, this behaviour can be understood as a manifestation of teleological features of physics. I will also introduce several formal mathematical frameworks that have been used to analyse contextuality and discuss how their results should be interpreted.

A local-realistic theory for fermions

Papers QISS1 / By

We propose a local model for general fermionic systems, which we express in the Heisenberg picture. To this end, we shall use a recently proposed formalism, the so-called “Raymond-Robichaud” construction, which allows one to construct an explicitly local model for any dynamical theory that satisfies no-signalling, in terms of equivalence classes of transformations that can be attached to each individual subsystem. By following the rigorous use of the parity superselection rule for fermions, we show how this construction removes the usual difficulties that fermionic systems display in regard to the definition of local states and local transformations.