Quantum Physics

Measurement is a fundamental ingredient of quantum theory, and reasonably well-understood in non-relativistic quantum mechanics. In contrast, relativistic requirements of locality and causality have provided a challenge for measurement in quantum field theory, as highlighted by Sorkin's seminal work. A second challenge is compositionality: Instead of the simple linear composition in terms of temporal order of the non-relativistic setting, we want to describe joint measurements arbitrarily distributed over different regions of spacetime. A third challenge is that we want to describe the measurement of specific observables and allow for time-extended observables. Progress on the first challenge has been made mostly in an ancilla setting, where an additional system is introduced that models a measurement apparatus. Instead, I focus in this talk on recent results that show how all three challenges can be addressed at a fundamental level.