  We quantify correlations (quantum and/or classical) between two continuous
variable modes in terms of how many correlated bits can be extracted by
measuring the sign of two local quadratures. On Gaussian states, such `bit
quadrature correlations' majorize entanglement, reducing to an entanglement
monotone for pure states. For non-Gaussian states, such as photonic Bell
states, ideal and real de-Gaussified photon-subtracted states, and mixtures of
pure Gaussian states, the bit correlations are shown to be a {\em monotonic}
function of the negativity. This yields a feasible, operational way to
quantitatively measure non-Gaussian entanglement in current experiments by
means of direct homodyne detection, without a full tomographical reconstruction
of the Wigner function.
