Quantum nondemolition measurements in systems with nonstationarity squeezing of quantum noise

A Weber detector with optical readout systems is considered. The measuring device consists of circulators, homodyne detector and two degenerate parametric amplifiers (or four wave mixers), modifying vacuum fluctuations of the load. In this scheme the greater the squeezing of back-action noise, the smaller the measurable force acting on the mechanical resonator. Postulation of gedanken state reduction is not necessary in our model