NO CLONING OF ORTHOGONAL STATES IN COMPOSITE SYSTEMS

The no-cloning principle tells us that nonorthogonal quantum states ca nnot be cloned, but it does not tell us that orthogonal states can alw ays be cloned. We suggest a situation where the cloning transformation s an restricted, leading to a novel type of no-cloning principle. In t he case of a composite system made of two subsystems: if the subsystem s are only available one after the other then there are various cases when orthogonal states cannot be cloned. Surprising examples are given , which give a radically better insight regarding the basic concepts o f quantum cryptography.