Unified Approach to Universal Cloning and Phase-Covariant Cloning
  We analyze the problem of approximate quantum cloning when the quantum state is between two latitudes on the Bloch's sphere. We present an analytical formula for the optimized 1-to-2 cloning. The formula unifies the universal quantum cloning (UQCM) and the phase covariant quantum cloning. 
Jia-Zhong Hu, Zong-Wen Yu, Xiang-Bin Wang