  A beam splitter can generate entanglement if the input field is nonclassical,
e.g. squeezed. Thus, beam splitter transformation can be utilized for obtaining
single-mode nonclassicality conditions from two-mode entanglement criteria.
Here, we demonstrate that (i) the generalized quadrature-squeezing condition
$\langle\hat{a}^\dagger\hat{a}\rangle < |\langle \hat{a}^2\rangle|$ can be
obtained from the two-mode entanglement criterion of
Duan-Giedke-Cirac-Zoller~[PRL 84, 2722]. (ii) Single-mode nonclassicality
condition, obtained from the two-mode entanglement criterion of Simon~[PRL, 84
2726], can detect (also accompanies) the nonclassicality of a superradiant
ground state where no quadrature-squeezing takes place. (iii) We present an
explicit form for a single-mode nonclassicality measure, for Gaussian states,
via maximization of the beam splitter output with respect to the beam splitter
parameters. We measure the nonclassicality of a squeezed state and the one
generated by a damped second harmonic crystal cavity. We determine pump
strengths where single-mode nonclassicality onsets, i.e. resists against the
vacuum noise.
