Heisenberg Operator Approach for Spin Squeezing Dynamics
  We reconsider the one-axis twisting Hamiltonian, which is commonly used for generating spin squeezing, and treat its dynamics within the Heisenberg operator approach. To this end we solve the underlying Heisenberg equations of motion perturbatively and evaluate the expectation values of the resulting time-dependent Heisenberg operators in order to determine approximately the dynamics of spin squeezing. Comparing our results with those originating from exact numerics reveals that they are more accurate than the commonly used frozen spin approximation. 
Aranya B. Bhattacherjee, Deepti Sharma and Axel Pelster
cond-mat.quant-gas quant-ph