Quantum reference frames: a relational perspective on nonclassical spacetime

Understanding the fundamental nature of gravity at the interface with quantum theory is a major open question in theoretical physics. Recently, the study of gravitating quantum systems, namely quantum systems sourcing a gravitational field and interacting gravitationally, has attracted a lot of attention, thanks to the possibility of realising these scenarios in the laboratory in the near future. When a quantum system sources a gravitational field, spacetime is fundamentally nonclassical. In this situation, also the notion of a reference frame needs to be generalised to account for quantum features of spacetime, thus realising a quantum reference frame (QRF). In this talk, I will introduce a formalism to associate a QRF to the quantum state of a particle, and show examples of why QRFs can contribute to formulate physics on nonclassical spacetime.