Quantum theory of an active interferometer

An investigation is reported of the influence of quantum noise of amplifying and absorbing media in an active interferometer, excited by an external signal, on its output characteristics. The amplitude and the frequency of the external signal are assumed to be constant. A quantum description of the radiation emitted by an active interferometer is provided by a method involving the use of coherent states. A quantum kinetic equation is derived for the distribution function of the amplitude and phase of the field in an active interferometer and the corresponding diffusion coefficients are found. The variances of fluctuations of the energy of the field and its phase, and also the spectral densities of the fluctuations, are calculated.