The entanglement manifold as the characteristic of compound quantum systems: the case of two qubits

The conception of entanglement manifold En for quantum system is proposed. Mathematically it is defined as coset space of Hilbert space full system over Cartesian product of Hilbert spaces of subsystems. In the case of two qubits the analytical description of manifold E2 is developed. The questions of interrelation of entanglement manifold with properties and measure of entanglement of a quantum mechanical system are discussed.