Quantum interference of “clocks" and Unruh-deWitt detectors

A major goal of modern physics is to understand and test the regime where quantum mechanics and general relativity both play a role. A promising path towards this goal is to study low-energy but composite quantum particles subject to relativistic effects. The reason is that such particles can model ideal clocks — their internal degrees of freedom measure proper time along the particle’s world line, as well as Unruh-deWitt detectors — when interactions of the internal degrees of freedom with an external quantised field are included. I will discuss what foundational insights into the notions of time, causality and thermalisation are enabled by this approach, specifically looking at the interference effects arising when a quantum clock or an Unruh-deWitt detector follows in superposition different spacetime trajectories.