Efficient classical simulation of measurements in optical quantum   information
  We present conditions for the efficient simulation of a broad class of optical quantum circuits on a classical machine: this class includes unitary transformations, amplification, noise, and measurements. Various proposed schemes for universal quantum computation using optics are assessed against these conditions, and we consider the minimum resource requirements needed in any optical scheme to generate optical nonlinear processes and perform universal quantum computation. 
Stephen D. Bartlett and Barry C. Sanders