  We examine quantum detection via a Michelson interferometer embedded in a gas
with Kerr nonlinearity. This nonlinear interferometer is illuminated by pulses
of classical light. This strategy combines the robustness against practical
imperfections of classical light with the improvement provided by nonlinear
processes. Regarding ultimate quantum limits, we stress that, as a difference
with linear schemes, the nonlinearity introduces pulse duration as a new
variable into play along with the energy resources.
