Holographic properties of superposed quantum geometries

TL;DR

This paper investigates the holographic properties of superposed quantum geometries using tensor networks, revealing conditions for isometric mappings and advancing quantum gravity tensor network models.

Contribution

It introduces an algebraic approach to holography for superposed quantum geometries, extending tensor network techniques to non-factorizing Hilbert spaces in quantum gravity.

Findings

Bulk-to-boundary maps are isometric only for fixed total boundary area.

Average properties of superposed geometries exhibit typicality in information transport.

Nontrivial area operators dominate entropy calculations in these quantum geometries.

Abstract

We study the holographic properties of a class of quantum geometry states characterized by a superposition of discrete geometric data, in the form of generalised tensor networks. This class specifically includes spin networks, the kinematic states of lattice gauge theory and discrete quantum gravity. We employ an algebraic, operatorial definition of holography based on quantum information channels, an approach which is particularly valuable in settings, such as the one we consider, where the relevant Hilbert space of states does not factorize into subsystem Hilbert spaces due to gauge invariance. We apply random tensor network techniques (successfully used in the AdS/CFT context) to analyse information transport properties of the bulk-to-boundary and boundary-to-boundary maps associated with this superposition of quantum geometries, and produce typicality results about the average over the geometric data colouring the fixed graph structure. In this context, one naturally obtains a nontrivial area operator encoding the dominant contribution to entropy calculations. Among our main results is the requirement that one can only isometrically map a bulk region onto boundaries with fixed total area. We furthermore inquire about similar state-induced mappings between segments of the boundary, and discuss related conditions for isometric behaviour. These generalisations make further steps towards quantum gravity implementations of tensor network holography.