Eur. Phys. J. D 57, 293-300 (2010)
https://doi.org/10.1140/epjd/e2010-00032-9

High-fidelity copies from a symmetric 1→2 quantum cloning machine

¹ Max-Planck-Institut für Kernphysik, Postfach 103980, 69029 Heidelberg, Germany
² Physikalisches Institut, Heidelberg Universität, 69120 Heidelberg, Germany
³ Department of Physical Sciences, P.O. Box 3000, University of Oulu, 90014 Oulu, Finland
⁴ Frankfurt Institute for Advanced Studies, 60438 Frankfurt am Main, Germany

Corresponding author: siomau@physi.uni-heidelberg.de

Received: 15 December 2009
Revised: 25 January 2010
Published online: 16 February 2010

Abstract

A symmetric 1→2 quantum cloning machine (QCM) is presented that provides high-fidelity copies with 0.90≤ F≤0.95 for all pure (single-qubit) input states from a given meridian of the Bloch sphere. Emphasize is placed especially on the states of the (so-called) Eastern meridian, that includes the computational basis states |0〉,|1〉 together with the diagonal state , for which suggested cloning transformation is shown to be optimal. In addition, we also show how this QCM can be utilized for eavesdropping in Bennett's B92 protocol for quantum key distribution with a substantial higher success rate than obtained for universal or equatorial quantum copying.