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.
@article{arxiv.0804.4207,
title = {Unified Approach to Universal Cloning and Phase-Covariant Cloning},
author = {Jia-Zhong Hu and Zong-Wen Yu and Xiang-Bin Wang},
journal= {arXiv preprint arXiv:0804.4207},
year = {2008}
}