Second-quantized Unruh-DeWitt detectors and their quantum reference frame transformations

We generalize the Unruh-DeWitt detector model to second quantization. illustrate this by applying it an excited particle in a superposition of relativistic velocities. calculate, first order, how its decay depends on whether velocities is coherent or incoherent. Further, we framework quantum reference frames allow transformations rest second-quantized Unruh DeWitt detectors. As application, show transform into frame decaying that, laboratory frame, linear relativistically differing