  In the recent experimental and theoretical literature well-established
nonclassicality criteria from the field of quantum optics have been directly
applied to the case of excitations in matter-waves. Among these are violations
of Cauchy-Schwarz inequalities, Glauber-Sudarshan P-nonclassicality,
sub-Poissonian number-difference squeezing (also known as the two-mode
variance) and the criterion of nonseparability. We review the strong connection
of these criteria and their meaning in quantum optics, and point out
differences in the interpretation between light and matter waves. We then
calculate observables for a homogenous Bose-Einstein condensate undergoing an
arbitrary modulation in the interaction parameter at finite initial
temperature, within both the quantum theory as well as a classical reference.
We conclude that to date in experiments relevant for analogue gravity,
nonclassical effects have not conclusively been observed and conjecture that
additional, noncommuting, observables have to be measured to this end.
