  We discuss generic spin squeezing operators (quadratic in angular momentum
operators) capable of squeezing out quantum mechanical noise from a system of
two-level atoms (spins) in a coherent state. Such systems have been considered
by Kitagawa and Ueda (Refs. 2) in this context and a Hamiltonian of this nature
governs the Lipkin model (Ref. 14) which is relevant to nuclear physics.
