A new representation for the density matrix

Abstract

A new method of writing the density matrix for higher-spin systems in terms of the generators of the group SU(n) is proposed. This leads to the definition of a set of new statistical tensors. Two basis advantages of this new method are that it can handle both the cases of oriented as well as non-oriented spin systems with equal facility and that it leads to simple bounds on the new statistical tensors. These bounds are explicitly studied for spin-1 and spin-3/2 systems and compared with the bounds obtained earlier by Minnaert and Dalitz. The equivalence of this method to the description in terms of the Fano statistical tensors, in the particular case of oriented systems, is also established.