Positive maps of density matrix and a tomographic criterion of entanglement

The positive and not completely positive maps of density matrices are discussed. Probability representation of spin states (spin tomography) is reviewed and U(N)-tomogram of spin states is presented. Unitary U(∞)-group tomogram of photon state in Fock basis is constructed. Notion of tomographic purity of spin states is introduced. An entanglement criterion for multipartite spin-system is given in terms of a function depending on unitary group parameters and semigroup of positive map parameters. Some two-qubit and two-qutrit states are considered as examples of entangled states using depolarizing map semigroup