After a general review of the analysis already available for back-action evasion schemes a perturbative approach is introduced and applied to a simple case. As a generalization of the back-action evasion schemes the concept of optimal pumping spectrum is introduced: it works for a unified treatment of stroboscopic and continuous quantum nondemolition strategies. Generalized back-action evasion strategies are introduced and studied in simple applications: they open the possibility for developing high-sensitivity schemes for the measurements of small forces. In particular, estimates of the noise figure for generalized back-action evasion transducers are discussed in detail.

• Received 13 August 1990

DOI:https://doi.org/10.1103/PhysRevA.43.2113