Quantum Cloning and Multiphoton

Tsuyoshi Nishioka, Hasegawa, Toshio, Hirokazu Ishizuka

Multiphoton state in quantum cryptography decreases its security. Key disclosing with universal quantum cloning machine (UQCM) is considered in explicit manner. Although UQCM cannot make perfect clones, there is some invariant quantity between the original photon and the imperfect clones. The invariant quantity, the direction of Stokes parameters, tells us the auxiliary information leading into key information. The attack, then, corresponds to some kind of quantum non-demolition measurement. Its application to recent high-performance quantum cryptography, Y-00 protocol, is also studied.

Nicolas J. Cerf, Jaromı́r Fiurášek

Sadegh Raeisi, Wolfgang Tittel, Christoph Simon

Marco B. Caminati, F. De Martini, Fabio Sciarrino

We investigate multiphoton states generated by high-gain optical parametric amplification of a single injected photon—polarization encoded as a qubit. The experimental configuration exploits the optimal phase-covariant cloning. The output state of the apparatus is found to exhibit the quantum superposition property of mesoscopic multiphoton assemblies involving about 300 photons. This work represents an experimental advance toward the test of several fundamental quantum processes in mesoscopic or macroscopic frameworks.

Nicolas Gisin

Aleksandr V. Belinsky, A. P. Grigorieva, Джадан Игорь Иванович

The possibility of multiphoton teleportation with the production of entangled particle clones has been studied. Issues of causality in quantum teleportation have been considered.