  We study interferometry with Gaussian states and show that an
ancilla-assisted scheme outperforms coherent state interferometry for all
levels of loss. We also compare the ancilla-assisted scheme to other
interferometric schemes involving squeezing, and show that it is the most
advantage in the high-loss, high photon-number regime. In fact, in the presence
of high loss, it out-performs many other strategies proposed to date. We find
the optimal measurement observable for each scheme discussed. We also find that
with the appropriate measurement, the achievable precision of the proposal by
Caves [Phys. Rev. D 23, 1693 (1981)] can be improved upon, and is less
vulnerable to losses than previously thought.
