Unpolarized light in quantum optics
  We present a new derivation of the unpolarized quantum states of light, whose general form was first derived by Prakash and Chandra [Phys. Rev. A 4, 796 (1971)]. Our derivation makes use of some basic group theory, is straightforward, and offers some new insights. 
Jonas Soderholm, Gunnar Bjork and Alexei Trifonov