We show that optimal universal quantum cloning can be realized via stimulated emission. Universality of the cloning procedure is achieved by choosing systems that have appropriate symmetries. We first discuss a scheme based on stimulated emission in certain three-level-systems, e.g. atoms in a cavity. Then we present a way of realizing optimal universal cloning based on stimulated parametric down-conversion. This scheme also implements the optimal universal NOT operation.
@article{arxiv.quant-ph/9910048,
title = {Optimal Quantum Cloning via Stimulated Emission},
author = {Christoph Simon and Gregor Weihs and Anton Zeilinger},
journal= {arXiv preprint arXiv:quant-ph/9910048},
year = {2009}
}