Abstract
We consider various configuration of quantum-enhanced interferometers, both linear (SU(2)) and non-linear (SU(1,1)) ones, as well as hybrid SU(2)/SU(1,1) schemes. Using the unified modular approach, based on the Quantum Cramer-Rao bound, we show that in all practical cases, their sensitivity is limited by the same equations (95) or (97) which first appeared in the pioneering work by C.Caves [Phys.Rev.D 23, 1693 (1981)].