Biomedical subjects
Publications and source records attributed to S Iblisdir.
We assess the security of a quantum key distribution protocol relying on the transmission of Gaussian-modulated coherent states and homodyne detection. This protocol is shown to be equivalent to an entanglement purification protocol using CSS codes followed by key extraction, and is thus secure against any eavesdropping strategy.
A quantum cloning machine is introduced that yields M identical optimal clones from N replicas of a coherent state and N' replicas of its phase conjugate. It also optimally produces M' = M+N'-N phase-conjugate clones at no cost. For well chosen ratios N'/N, this machine is shown to provide better cloning fidelities than the standard (N+N')-->M cloner. The special cases of the optimal balanced cloner (N = N') and optimal measurement (M = infinity) are investigated.
A transformation achieving the optimal symmetric N-->M cloning of coherent states is presented. Its implementation requires only a phase-insensitive linear amplifier and a network of beam splitters. An experimental demonstration of this continuous-variable cloner should therefore be in the scope of current technology. The link between optimal quantum cloning and optimal amplification of quantum states is also pointed out.