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Abstract:  In relativity, the geometry of the light cones determines the causal structure of spacetime. Under the influence of gravity, the light cones bend and curve. A previously expanding light cone can fall back into itself. In this way, the causal structure becomes a dynamical aspect of spacetime. How do we understand this link between gravity, geometry and causality at the quantum level? Is there a quantum light cone geometry? In my talk, I will argue that the answer to this problem is crucial for making progress in quantum gravity. It is, in fact, a problem that is shared among different approaches, from holography, to celestial amplitudes and loop quantum gravity. In my presentation, I report on three new results on this frontier. First, I provide a non-perturbative characterization of impulsive gravitational null initial data for tetradic gravity on a light cone. Second, the description is taken to the quantum level. Third, an immediate physical implication is found: in the model, the Planck luminosity separates the eigenvalues of the radiated power. Below the Planck power, the spectrum of the radiated power is discrete. Above the Planck power, the spectrum is continuous and the resulting physical states contain caustics that can spoil the semi-classical limit.  The talk is based on arXiv:2402.12578, arXiv:2401.17491, arXiv:2104.05803.

Entanglement in quantum many-body systems is typically fragile to interactions with the environment. Generic unital quantum channels, for example, have the maximally mixed state with no entanglement as their unique steady state. However, we find that for a unital quantum channel that is `strongly symmetric', i.e. it preserves a global on-site symmetry, the maximally mixed steady state in certain symmetry sectors can be highly entangled. For a given symmetry, we analyze the entanglement and correlations of the maximally mixed state in the invariant sector (MMIS), and show that the entanglement of formation and distillation are exactly computable and equal for any bipartition. For all Abelian symmetries, the MMIS is separable, and for all non-Abelian symmetries, the MMIS is entangled. Remarkably, for non-Abelian continuous symmetries described by compact semisimple Lie groups (e.g. SU(2)), the bipartite entanglement of formation for the MMIS scales logarithmically ∼logN with the number of qudits N.

About the Event:

Perimeter Presents

About the Speaker:

Most people have a basic understanding of gravity as the fundamental force that keeps us tethered to the Earth. They've likely even heard the fabled story of Isaac Newton’s inspiration for the theory: an apple falling from a tree. But few people have spent as much time grappling with gravity as Claudia de Rham, Professor of Theoretical Physics at Imperial College London.

In her recently released book, The Beauty of Falling: A Life in Pursuit of Gravity, de Rham recounts not only her scientific investigations of gravity and the limits of Einstein’s general theory of relativity, but also her more practical encounters with gravity – as a diver, a pilot, and an astronaut candidate.

Many of de Rham’s ponderous flights took place in Waterloo Region, where she earned her pilot’s license during a postdoctoral fellowship at Perimeter from 2006 to 2009. She has remained connected to Perimeter over the years, including as a Visiting Fellow since 2018.

About the Event:

On Thursday, August 1 at 7:00 PM EDT, Perimeter presents a short talk with de Rham about her fascinating journey in pursuit of gravity’s true nature, followed by an in-depth conversation with Nahlah Ayed, host of CBC’s Ideas, and an audience Q&A.

Tickets:

Registration to attend this in-person event will be available on Monday, July 22 at 9:00 AM EDT.

Eventbrite

This event will not be livestreamed, but made available in the subsequent days on Perimeter’s YouTube channel. An edited version will also appear on CBC’s Ideas in the fall.

Tickets for this event are 100% free.