Spin squeezing by tensor twisting and Lipkin-Meshkov-Glick dynamics in a   toroidal Bose-Einstein condensate with spatially modulated nonlinearity
  We propose a scheme for spin-squeezing in the orbital motion of a Bose-Einstein condensate (BEC) in a toroidal trap. A circular lattice couples two counter-rotating modes and squeezing is generated by the nonlinear interaction spatially modulated at half the lattice period. By varying the amplitude and phase of the modulation, various cases of the twisting tensor can be directly realized, leading to different squeezing regimes. These include one-axis twisting and the two-axis counter-twisting which are often discussed as the most important paradigms for spin squeezing. Our scheme naturally realizes the Lipkin-Meshkov-Glick model with the freedom to vary all its parameters simultaneously. 
Tom\'a\v{s} Opatrn\'y, Michal Kol\'a\v{r} and Kunal K. Das
cond-mat.quant-gas quant-ph