NONLINEAR QUANTUM STATE TRANSFORMATION OF SPIN-1 2/

A non-linear quantum scare transformation is presented. The transforma tion, which operates on pairs of spin-1/2, can be used to distinguish optimally between two non-orthogonal states. Similar transformations a pplied locally on each component of an entangled pair of spin-1/2 can be used to transform a mixed non-local state into a quasi-pure maximal ly entangled singlet state. In both cases the transformation makes use of the basic building block of the quantum computer, namely the quant um-XOR gale. (C) 1998 Elsevier Science B.V.