On a quantum model of a laser-interferometer measuring a weak classical   force
  We consider a solvable model of a laser-interferometer measuring a weak classical force. The model takes into account dissipation of the energy by transfer to the environment at zero temperature. The sensitivity (the signal-to-noise ratio) of the device is defined as the corresponding ratio between the mean value and the variance of a certain observable. We analyze the dependence of the sensitivity upon the duration of the measurement and the photon number. For parameters typical for the LIGO project, we discuss numerical estimates. 
A. M. Sinev (Bauman Moscow State Technical University, Moscow, Russia)