Speaker
Description
Reference frames play an important role in any theory with a symmetry, from simple translationally invariant models to full general relativity. Taking into account the quantum properties of the systems that we use as reference frames leads to the study of quantum reference frames (QRFs). There are different approaches to QRFs, some mirroring the structure of constraint quantisation, while others focus more on operational considerations from quantum information. All of the approaches share one feature, though: subsystem relativity. That is, how we partition the Hilbert space into different subsystems depends on the choice of QRF. Subsystem relativity has many interesting consequences, such as the relativity of entanglement, entropy, and coherence. In this talk, I will use a simple toy model at the intersection between quantum theory and gravity to take a look at one particular consequence, the relativity of decoherence, and discuss its operational meaning. Moreover, studying states which leave the subsystem structure invariant, we will find a close connection to the constraint generating the symmetry group, which suggests a natural extension of the QRF formalism to non-zero charge sectors for abelian symmetry groups.