Analytical solution to the quantum field theory of self-phase modulation with a finite response time

Abstract
The quantum theory of a field in 1+1 dimensions coupled to localized oscillators is developed. The solution to the Heisenberg equation for the field is given in closed form. It is shown that the nonlinearity of the medium is inevitably accompanied by phase noise of the field. This noise explains the preferential growth of the Stokes wave for short propagation distances.