title: Non-Gaussian cloning of quantum coherent states is optimal.
abstract: We consider the optimal cloning of quantum coherent states with single-clone and joint fidelity as figures of merit. While the latter is maximized by a Gaussian cloner, the former is not: the optimal single-clone fidelity for a symmetric 1-to-2 cloner is 0.6826, compared to 2/3 in a Gaussian setting. This cloner can be realized with an optical parametric amplifier and certain non-Gaussian bimodal states. Finally, we show that the single-clone fidelity of the optimal 1-to-infinity cloner is 1/2. It is achieved by a Gaussian scheme and cannot be surpassed even with supplemental bound entangled states.
authors.affiliation: QUIC, Ecole Polytechnique, CP 165, Université Libre de Bruxelles, Belgium.
authors.forename: N J
authors.initials: NJ
authors.lastname: Cerf
authors.forename: O
authors.initials: O
authors.lastname: Krüger
authors.forename: P
authors.initials: P
authors.lastname: Navez
authors.forename: R F
authors.initials: RF
authors.lastname: Werner
authors.forename: M M
authors.initials: MM
authors.lastname: Wolf