Special relativity and reduced spin density matrices
Cezary Gonera, Piotr Kosiński, Paweł Maślanka · Physical Review A · 2004
We derive the general formula for Lorentz-transformed spin density matrix. It is shown that an appropriate Lorentz transformation can produce totally unpolarized state out of pure one. Further properties, as depurification by an arbitrary Lorentz boost and its relation to the localization properties are also discussed.