Quantum theory of fluctuations in a cold damped accelerometer

We present a quantum network approach to real high sensitivity measurements . Thermal and quantum fluctuations due to active as well as passive element s are taken into account. The method is applied to the analysis of the capa citive accelerometer using the cold damping technique, developed for fundam ental physics in space by ONERA and the ultimate limits of this instrument are discussed. It is confirmed in this quantum analysis that the cold dampi ng technique allows one to control efficiently the test mass motion without degrading the noise level.