Quantum back-action in spinor condensate magnetometry
  We provide a theoretical treatment of the quantum backaction of Larmor frequency measurements on a spinor Bose-Einstein condensate by an off-resonant light field. Two main results are presented; the first is a "quantum jump" operator description that reflects the abrupt change in the spin state of the atoms when a single photon is counted at a photodiode. The second is the derivation of a conditional stochastic master equation relating the evolution of the condensate density matrix to the measurement record. We comment on applications of this formalism to metrology and many-body studies. 
S. K. Steinke, S. Singh, P. Meystre, K. C. Schwab, M. Vengalattore
quant-ph cond-mat.quant-gas