Application of the no-signaling principle to obtain quantum cloners for   any allowed value of fidelity
  Special relativity forbids superluminal influences. Using only the no-signaling principle and an assumption about the form of the Schmidt decomposition, we show that for "any" allowed fidelity there is a "unique" approximate qubit cloner which can be written explicitly. We introduce the prime cloners whose fidelities have multiplicative property and show that the fidelity of the prime cloners for the infinite copy limit is 1/2. 
Z. Gedik and B. \c{C}akmak
quant-ph