Precision Measurements Using Squeezed Spin States via Two-axis   Counter-twisting Interactions
  We show that the two-axis counter twisting interaction squeezes a coherent spin state into three states of interest in quantum information, namely, the twin-Fock state, the equally-weighted superposition state, and the state that achieves the Heisenberg limit of optimal sensitivity defined by the Cramer-Rao inequality in addition to the well-known Heisenberg-limited state of spin fluctuations. 
Emi Yukawa, Gerard Milburn, Masahito Ueda, and Kae Nemoto
quant-ph