Скачать или смотреть Robert Oeckl: Measurement in quantum field theory: Local, causal and compositional

Measurement is reasonably well-understood in non-relativistic quantum mechanics. However, relativistic requirements of locality, causality and no-signaling have provided challenges for measurement in quantum field theory. We recall some of these challenges, especially as uncovered in Sorkin's seminal work. Progress has been made mostly in an ancilla setting, where an additional system is introduced that models a measurement apparatus. The actual measurement on the apparatus then falls back to the standard non-relativistic prescription. Instead, I focus in this talk on recent results that show how the challenges can be addressed at a fundamental level. This also involves a question of quantization, i.e., how to construct the (generalized) quantum operation that implements the measurement of a given observable. Another key issue I address is compositionality: If we can do several different measurements in different spacetime regions then we can also do the joint measurement and the formalism has to reflect this.