  We propose a feedback scheme for the production of two-mode spin squeezing.
We determine a general expression for the optimal feedback, which is also
applicable to the case of single-mode spin squeezing. The two-mode spin
squeezed states obtained via this feedback are optimal for j=1/2 and are very
close to optimal for j>1/2. In addition, the master equation suggests a
Hamiltonian that would produce two-mode spin squeezing without feedback, and is
analogous to the two-axis countertwisting Hamiltonian in the single mode case.
