  We propose an experimentally accessible procedure for conditional preparation
of highly non-classical states of collective spin of an atomic ensemble. The
quantum state engineering is based on a combination of QND interaction between
atoms and light previously prepared in a non-Gaussian state using photon
subtraction from squeezed vacuum beam, homodyne detection on the output light
beam, and a coherent displacement of atomic state. The procedure is capable of
non-deterministic preparation of a wide class of superpositions of atomic Dicke
states. We present several techniques to optimize the performance of the
protocol and maximize the trade-off between fidelity of prepared state and
success probability of the scheme.
