Entanglement enhancement is a key task for quantum technologies.
This operation performed on states produced by
parametric down-conversion sources has been the object of
several recent experimental investigations. In particular, conditional
preparation by photon-subtraction has been shown to
improve the entanglement of these states. Here we analyse
the role played by non-Gaussian and Gaussian measurements
in more general entanglement concentration operations
performed on a pair of two-mode squeezed vacua.
We find stringent requirements for achieving an improved entanglement
enhancement by measuring jointly these two resource