Measurement back-action on the quantum spin-mixing dynamics of a spin-1   Bose-Einstein condensate
  We consider a small F=1 spinor condensate inside an optical cavity driven by an optical probe field, and subject the output of the probe to a homodyne detection, with the goal of investigating the effect of measurement back-action on the spin dynamics of the condensate. Using the stochastic master equation approach, we show that the effect of back-action is sensitive to not only the measurement strength but also the quantum fluctuation of the spinor condensate. The same method is also used to estimate the atom numbers below which the effect of back-action becomes so prominent that extracting spin dynamics from this cavity-based detection scheme is no longer practical. 
Keye Zhang, Lu Zhou, Hong Y. Ling, Han Pu, Weiping Zhang
quant-ph cond-mat.quant-gas