Fundamental limits on quantum cloning from the no-signalling principle

Abstract

The no-cloning theorem is a cornerstone of quantum cryptography. Here we generalize and rederive in a unified framework various upper bounds on the maximum achievable fidelity of probabilistic and deterministic cloning machines. Building on ideas by Gisin [Phys.~Lett.~A, 1998], our result starts from the fact that remote state preparation is possible and the no-signalling principle holds. We apply our general theorem to several subsets of states that are of interest in quantum cryptography.