5,136 research outputs found
Optimal multicopy asymmetric Gaussian cloning of coherent states
We investigate the asymmetric Gaussian cloning of coherent states which
produces M copies from N input replicas, such that the fidelity of all copies
may be different. We show that the optimal asymmetric Gaussian cloning can be
performed with a single phase-insensitive amplifier and an array of beam
splitters. We obtain a simple analytical expression characterizing the set of
optimal asymmetric Gaussian cloning machines.Comment: 7 pages, 2 figures, RevTeX
A lower bound on the two-arms exponent for critical percolation on the lattice
We consider the standard site percolation model on the -dimensional
lattice. A direct consequence of the proof of the uniqueness of the infinite
cluster of Aizenman, Kesten and Newman [Comm. Math. Phys. 111 (1987) 505-531]
is that the two-arms exponent is larger than or equal to . We improve
slightly this lower bound in any dimension . Next, starting only with
the hypothesis that , without using the slab technology, we derive
a quantitative estimate establishing long-range order in a finite box.Comment: Published at http://dx.doi.org/10.1214/14-AOP940 in the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Cloning a Qutrit
We investigate several classes of state-dependent quantum cloners for
three-level systems. These cloners optimally duplicate some of the four
maximally-conjugate bases with an equal fidelity, thereby extending the
phase-covariant qubit cloner to qutrits. Three distinct classes of qutrit
cloners can be distinguished, depending on two, three, or four
maximally-conjugate bases are cloned as well (the latter case simply
corresponds to the universal qutrit cloner). These results apply to symmetric
as well as asymmetric cloners, so that the balance between the fidelity of the
two clones can also be analyzed.Comment: 14 pages LaTex. To appear in the Journal of Modern Optics for the
special issue on "Quantum Information: Theory, Experiment and Perspectives".
Proceedings of the ESF Conference, Gdansk, July 10-18, 200
Cloning quantum entanglement in arbitrary dimensions
We have found a quantum cloning machine that optimally duplicates the
entanglement of a pair of -dimensional quantum systems. It maximizes the
entanglement of formation contained in the two copies of any
maximally-entangled input state, while preserving the separability of
unentangled input states. Moreover, it cannot increase the entanglement of
formation of all isotropic states. For large , the entanglement of formation
of each clone tends to one half the entanglement of the input state, which
corresponds to a classical behavior. Finally, we investigate a local
entanglement cloner, which yields entangled clones with one fourth the input
entanglement in the large- limit.Comment: 6 pages, 3 figure
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