Speaker
Description
When describing a physical system, it is very common to do so with respect to a reference frame - a ruler used to determine the position of a particle, for example, or a clock, which tracks the time that elapses while it is moving. Usually, reference frames are treated as purely classical objects with well-defined properties. But what happens if we take into account the quantum properties of the reference frame itself? This question has motivated a recent wave of research on quantum reference frames (QRFs), which investigates how the description of our world changes when described relative to different quantum systems.
Changes of QRFs have a variety of interesting implications. Quantum features previously thought to be absolute, such as superposition and entanglement, suddenly become dependent on the frame. In fact, what we even mean by the same location, spin, or even subsystem across different branches of a superposition can change when describing the system with respect to different QRFs. Here, we introduce a generalized, visual framework that provides a deeper understanding of this phenomenon by relating the frame dependence to the fundamental question of how to identify and compare objects across a superposition. This becomes particularly relevant in the context of spacetimes in superposition, where there is a priori no notion of ”the same” or “different” points across the different possible worlds. With this newfound understanding, we explore the implications for scenarios at the interface between quantum physics and gravity, such as the gravitational field sourced by a massive object in superposition.
