It has been shown theoretically that a light amplifier working on the physical principle of stimulated emission should achieve optimal quantum cloning of the polarization state of light. We demonstrate close-to-optimal universal quantum cloning of polarization in a standard fiber amplifier for telecom wavelengths. For cloning 1 --> 2 we find a fidelity of 0.82, the optimal value being 5/6 = 0.83.
@article{arxiv.quant-ph/0203056,
title = {Quantum cloning with an optical fiber amplifier},
author = {Sylvain Fasel and Nicolas Gisin and Gregoire Ribordy and Valerio Scarani and Hugo Zbinden},
journal= {arXiv preprint arXiv:quant-ph/0203056},
year = {2009}
}