Practical schemes for the measurement of angular-momentum covariance   matrices in quantum optics
  We develop practical schemes for the measurement of the covariance matrix for intrinsic angular-momentum variables in quantum optics. We particularize this approach to two-beam polarimetry and interferometry, as well as to ensembles of two-level atoms interacting with classical fields. We show the practical advantages of noisy simultaneous measurements. 
\'Angel Rivas, Alfredo Luis