Środowiskowe Seminarium z Informacji i Technologii Kwantowych

The Wigner-Araki-Yanase (WAY) theorem delineates circumstances under which a class of quantum measurements is ruled out. Specifically, it states that any observable (given as a self adjoint operator) not commuting with an additive conserved quantity of a quantum system and measuring apparatus combined admits no repeatable measurements. I'll review the content of this theorem and present some new work which generalises and strengthens existing results. I'll tentatively discuss relativistic scenarios and comment on the role of quantum reference frames, raising some open questions in this area.