OPTIMAL RECONSTRUCTION OF EXTERNAL FORCES BELOW THE STANDARD QUANTUM LIMIT WITH PARAMETRIC NON-REGENERATIVE SYSTEMS

Detection and reconstruction of an external force acting on a parametr ic measuring system under standard quantum limit are considered. A non -stationary character of vacuum noise is an essential feature of param etric systems. Due to the parametric interaction of vacuum noise on th e signal and idler frequencies, the quadrature components of the outpu t signal are correlated. For optimal detection of an external force ac ting on such a system, one can use an optimal vector signal detection theory utilizing the correlation of quadrature components. A signal-to -noise ratio for force detection and the equivalent noise of force rec onstruction are estimated. To realize such measurements one has to use a phase-sensitive device and dual homodyne detector with proper local oscillator phase. Connection of the suggested algorithm with the pres criptions of the theory of quantum non-demolition measurements is disc ussed.