Degrees of polarization for a quantum field
Luis Lorenzo Sánchez-Soto, Jonas Söderholm, E. C. Yustas, A. B. Klimov, Gunnar G. Bjork · Journal of Physics Conference Series · 2006
Unpolarized light is invariant with respect to any SU(2) polarization transformation. Since this fully characterizes the set of density matrices representing unpolarized states, we introduce the degree of polarization of a quantum state as its distance to the set of unpolarized states. We discuss different candidates of distance, and show that they induce fundamentally different degrees of polarization.