Causal signal transmission by quantum fields. Quantum electrodynamics in   response representation
  Using electromagnetic interaction as an example, response transformations [L.P. and S.S., Ann.Phys. 323, 1963, 1989 (2008), 324, 600 (2009)] are applied to the standard perturbative approach of quantum field theory. This approach is rewritten in the form where the place of field propagators is taken by the retarded Green function of the field. Unlike in conventional quantum-field-theoretical techniques, the concept of space-time propagation of quantized field is built into our techniques. 
L.I.Plimak and S.T.Stenholm
quant-ph cond-mat.stat-mech hep-th math-ph math.MP