May 2025

Average entanglement entropy of a small subsystem in a constrained pure Gaussian state ensemble

We consider ensembles of pure Gaussian states parametrized by single-mode marginals and (optionally) specific mode-mode correlations. Such ensembles provide a model for the final states when isolated quantum systems thermalize, as they can reproduce thermal properties locally, while being globally pure. By an analysis using real replicas and the coherent state representation of Gaussian states we show that the average entanglement entropy of a small subsystem is the same as the von Neumann entropy of a mixed Gaussian state with the same marginals, but no correlations. Finally, we discuss how these ensembles provide a model for Hawking radiation assuming unitary evolution, and discuss some of their properties in relations to the Page curve of Hawking radiation.

Francesca Vidotto
Instituto de Estructura de la Materia (IEM-CSIC), Madrid, SpainSpinfoam Cosmology: Computing Spacetime Correlations From Scratch

Understanding the properties of a generic state given by the superposition of different spacetimes configuration is one of the major questions that quantum gravity aim to address. This has major implication for the physics of the early universe, where the seeds of cosmic structures are originated from quantum fluctuations of the geometry. Predicting the strength of correlations of geometrical observables in this regime gives direct access to the initial conditions of our universe, from which all matter structures later evolved.
Exploiting techniques from covariant Loop Quantum Gravity, I present an operational recipe to construct physical states of the quantum geometry, to define a cosmological interpretation for them, and compute analytically and numerically the quantities that characterize them, i.e. correlations between the volumes of spacially-separated region and the corresponding entanglement entropy. I review the results obtained and I discuss the future perspective of this research program.