  Recently, a non-Gaussian field, which may be a useful basis for entanglement
distillation and efficient quantum teleportation, has been experimentally
produced by subtracting a photon from a squeezed Gaussian field. We investigate
the nonclassicality of such the field using negativity in the Wigner function
and the existence of positive well-defined $P$ function. We obtain the
condition to see negativity in the Wigner function for the case including the
mixed Gaussian incoming field, the threshold photodetection and the inefficient
homodyne measurement. We show how similar the photon-subtracted state is to a
superposition of coherent states.
