We present a theoretical study of multi-mode scattering of light by optically random media, using the Mueller-Stokes formalism which permits to encode all the polarization properties of the scattering medium in a real $4 \times 4$ matrix. From this matrix two relevant parameters can be extracted: the depolarizing power $D_M$ and the polarization entropy $E_M$ of the scattering medium. By studying the relation between $E_M$ and $D_M$, we find that { \em all} scattering media must satisfy some { \em universal} constraints. These constraints apply to both classical and quantum scattering processes. The results obtained here may be especially relevant for quantum communication applications, where depolarization is synonymous with decoherence.
Categories: quant-ph