Measurement backaction on a spinor condensate from off-resonant light

We study the quantum backaction of spin precession imaging measurements on a Bose-Einstein condensate by off-resonant light. Two main results are the derivation of a quantum jump operator describing the small, abrupt change in the spin state of the atoms caused by the detection of a single photon and a conditional stochastic master equation for the evolution of the condensate subject to a particular measurement record. We examine the implications of these backaction effects for magnetometry and also evaluate their utility in quantum state preparation.