Speaker
Description
The so-called Sorkin's paradox manifests itself in QFT as the apparent presence of superluminal signalling, generating a conflict between the concept of measurement and locality. As a non-local transfer of information, it should have direct consequences for quantities like relative entropy. We analyse this phenomenon in the context of general algebraic QFT, where relative entropy may be quite generally expressed in terms of relative modular Hamiltonians, and we describe a scheme that allows to estimate relative modular Hamiltonians for suitable pairs of states on some local algebra in terms of modular Hamiltonians of a reference state on bigger or smaller algebras, which might be better understood.
For pairs of states susceptible to this scheme, there exist unitaries linking them to the reference state which do not enable superluminal signalling. Such unitaries may not however compose the whole class of non-signalling operators, raising the question whether the existence of a non-signalling unitary is a sufficient condition to show the applicability of our estimate. We comment on this issue using a construction involving the Cuntz algebra.
Based on a joint work with Christoph Minz and Ko Sanders.