Optimal universal entanglement processes are discussed which entangle two
quantum systems in an optimal way for all possible initial states. It is
demonstrated that the linear character of quantum theory which enforces the
peaceful coexistence of quantum mechanics and relativity imposes severe
restrictions on the structure of the resulting optimally entangled states.
Depending on the dimension of the one-particle Hilbert space such a universal
process generates either a pure Bell state or mixed entangled states. In the
limit of very large dimensions of the one-particle Hilbert space the
von-Neumann entropy of the optimally entangled state differs from the one of
the maximally mixed two-particle state by one bit only.Comment: Proceedings of the X International Symposium on Theoretical
Electrical Engineering, ISTET 99, Magdebur
