Speaker
Description
At the interface of quantum gravity and quantum information, growing evidence suggests that spacetime structure can be understood through quantum information-theoretic notions, with entanglement playing a central role. Yet, in the presence of gauge or diffeomorphism constraints, the notion of subsystems, crucial to define entanglement, becomes subtle: the Hilbert space does not factorize, and even when reduced density matrices can be defined, their von Neumann entropy does not capture operational entanglement.
I will argue that quantum reference frames (QRFs) provide a natural resolution of this problem. In lattice gauge theories, using internal degrees of freedom as reference frames, we can define relational subsystems (relative to the frame) that admit a clean Hilbert space factorization, together with a notion of distillable entanglement entropy. Different choices of frame give rise to a hierarchy of relational operator algebras, offering new insights into the role of edge modes, boundary symmetries, and observers in diffeomorphism-invariant systems, while recovering previous constructions within a unified perspective.