Abstract
We consider probabilistic cloning of a state chosen from a mutually nonorthogonal set of pure states, with the help of a party holding supplementary information in the form of pure states. When the number of states is 2, we show that the best efficiency of producing copies is always achieved by a two-step protocol in which the helping party first attempts to produce copies from the supplementary state, and if it fails, then the original state is used to produce copies. On the other hand, when the number of states exceeds two, the best efficiency is not always achieved by such a protocol. We give examples in which the best efficiency is not achieved even if we allow any amount of one-way classical communication from the helping party.
- Received 30 May 2005
DOI:https://doi.org/10.1103/PhysRevA.72.032335
©2005 American Physical Society