Principal Component Analysis of Quantum Correlation
  The concept of quantum correlation matrix for observables leads to the application of the PCA (Principal Component Analysis) also for quantum system in Hilbert space. It is shown that, in the case of a 2x2 spin system where the observables are the Pauli matrices and a polarization vector is acting on the density matrix, meaningful results can be obtained by the PCA in terms of qubit properties. In particular, it is shown that by choosing, for example, the (x,z) spinors, the axes of the principal components (PC) coincide with the circular polarization basis on the Block Sphere. 
Renzo Mosetti
quant-ph