Time evolution techniques for detectors in relativistic quantum   information
  The techniques employed to solve the interaction of a detector and a quantum field typically require perturbation methods. We introduce mathematical techniques to solve the time evolution of an arbitrary number of detectors interacting with a quantum field. Our techniques apply to harmonic oscillator detectors and can be generalized to treat detectors modeled by quantum fields. Since the interaction Hamiltonian we introduce is quadratic in creation and annihilation operators, we are able to draw from continuous variable techniques commonly employed in quantum optics. 
David Edward Bruschi and Antony R. Lee and Ivette Fuentes
quant-ph gr-qc