Temporal imperfections building up correcting codes

We address the timing problem in realizing correcting codes for quantum information processing. To deal with temporal uncertainties we employ a consistent quantum mechanical approach. The conditions for optimizing the effect of error correction in such a case are determined.Comment: 5 pages, 2 eps figures, to appear in J. Mod. Op

Information Dissipation in Random Quantum Networks

We study the information dynamics in a network of spin-$1/2$ particles when edges representing $XY$ interactions are randomly added to a disconnected graph accordingly to a probability distribution characterized by a "weighting" parameter. In this way we model dissipation of information initially localized in single or two qubits all over the network. We then show the dependence of this phenomenon from weighting parameter and size of the network.Comment: 9 pages, 5 figure

Quantum Zeno-like effect due to competing decoherence mechanisms

We propose a selfconsistent quantum mechanical approach to study the dynamics of a two-level system subject to random time evolution. This randomness gives rise to competing effects between dissipative and non-dissipative decoherence with a consequent slow down of the atomic decay rate.Comment: 4 pages, ReVTeX file, 2 eps figures, to appear in Phys. Rev.

Quantum Gaussian Channels with Additive Correlated Classical Noise

We provide a model to study memory effects in quantum Gaussian channels with additive classical noise over an arbitrary number of uses. The correlation among different uses is introduced by contiguous two-mode interactions. Numerical results for few modes are presented. They confirm the possibility to enhance the classical information rate with the aid of entangled inputs, and show a likely asymptotic behavior that should lead to the full capacity of the channel

Minimum output entropy of a non-Gaussian quantum channel

We introduce a model of non-Gaussian quantum channel that stems from the combination of two physically relevant processes occurring in open quantum systems, namely amplitude damping and dephasing. For it we find input states approaching zero output entropy, while respecting the input energy constraint. These states fully exploit the infinite dimensionality of the Hilbert space. Upon truncation of the latter, the minimum output entropy remains finite and optimal input states for such a case are conjectured thanks to numerical evidences