Speaker
Description
In quantum information theory, most standard notions depend crucially on how we partition the world into subsystems, a choice encoded in the tensor product structure of the Hilbert space. Yet, the subsystem structure has been shown to depend on the choice of quantum reference frame (QRF). This observation underlies many interesting features of QRFs, such as the relativity of entanglement, entropy, and coherence. It also raises a broader question: to what extent can quantum information measures be extended to regimes in which no fixed tensor product structure is available?
In this talk, we will address this question for quantum mutual information - the measure of the information that is “shared” between two systems. In order to formulate a notion of mutual information across different QRF perspectives, we focus on algebras of observables rather than tensor product structures - in line with the extension of these notions to quantum field theory. Moreover, we argue that it is advantageous to focus on information rather than entropy when working with more general subsystems. Based on these two observations, we propose a notion of mutual information between subsystems relative to different reference frames. Investigating this question not only sheds light on some important features of quantum information that also arise in recent discussions of the observer-dependence of gravitational entropy, but also provides a way to quantify what it means to be in the perspective of a QRF from an information-theoretic point of view.