And the abstract:
Title: An Operational Perspective on Non-Ideal Quantum Reference Frames
Abstract: Every physical observation is described relative to a reference frame. Reference frames are often treated as abstract entities, such as coordinate systems, whereas an operational approach to physics requires considering how reference frames are implemented with physical systems. When the objects serving as reference frames are quantum systems, this leads to the notion of Quantum Reference Frames (QRFs). Currently, a diversity of approaches have been developed to address the challenges posed by QRFs in quantum gravity and quantum information. In this talk, I will first review the perspective-neutral framework for QRFs, which provides internal descriptions of physical systems. I will then focus on non-ideal QRFs, constrained by finite resources or described by indistinguishable states. Next, I will discuss possible operational definitions of non-ideal QRFs within the perspective-neutral framework, distinguishing between definitions relative to an external frame and those relative to an internal one. Finally, I will present the condition for the Hilbert space, in a given QRF perspective, to factorize into the kinematical subsystems defined by the kinematical Hilbert space, where the QRF is defined as well. This imposes a necessary condition for an operational treatment of QRFs in the perspective-neutral approach, aiming to clarify the conceptual foundations of a relational and operational approach to QRFs.