  We address the use of entanglement to improve the precision of generalized
quantum interferometry, i.e. of binary measurements aimed to determine whether
or not a perturbation has been applied by a given device. For the most relevant
operations in quantum optics, we evaluate the optimal detection strategy and
the ultimate bounds to the minimum detectable perturbation. Our results
indicate that entanglement-assisted strategies improve the discrimination in
comparison with conventional schemes. A concrete setup to approach performances
of the optimal strategies is also suggested.
