Modelling a Particle Detector in Field Theory

Understand

Particle detector models allow to give an operational definition to the particle content of a given quantum state of a field theory.

• The commonly adopted Unruh-DeWitt type of detector is known to undergo temporary transitions to excited states even when at rest and in the Minkowski vacuum.
• We argue that real detectors do not feature this property, as the configuration "detector in its ground state + vacuum of the field" is generally a stable bound state of the underlying fundamental theory (e.g.
• the ground state-hydrogen atom in a suitable QED with electrons and protons) in the non-accelerated case.