Matrices of fidelities for ensembles of quantum states and the Holevo quantity

The entropy of the Gram matrix of a joint purification of an ensemble of K mixed states yields an upper bound for the Holevo information Chi of the ensemble. In this work we combine geometrical and probabilistic aspects of the ensemble in order to obtain useful bounds for Chi. This is done by constructing various correlation matrices involving fidelities between every pair of states from the ensemble. For K=3 quantum states we design a matrix of root fidelities that is positive and the entropy of which is conjectured to upper bound Chi. Slightly weaker bounds are established for arbitrary ensembles. Finally, we investigate correlation matrices involving multi-state fidelities in relation to the Holevo quantity.Comment: 24 pages, 3 figure

Noisy One-Way Quantum Computations: The Role of Correlations

A scheme to evaluate computation fidelities within the one-way model is developed and explored to understand the role of correlations in the quality of noisy quantum computations. The formalism is promptly applied to many computation instances, and unveils that a higher amount of entanglement in the noisy resource state does not necessarily imply a better computation.Comment: 10 pages, 6 figures, extension of a previous versio

Efficient and coherent excitation transfer across disordered molecular networks

We show that finite-size, disordered molecular networks can mediate highly efficient, coherent excitation transfer which is robust against ambient dephasing and associated with strong multi-site entanglement. Such optimal, random molecular conformations may explain efficient energy transfer in the photosynthetic FMO complex.Comment: 5 pages, 3 figures, revtex4-

A experiência brasileira de controlo da multidroga-resistência

AbstractIn this article the author reviews the evolution of the approach to multidrug-resistant tuberculosis (MDR-TB) in Brazil following the introduction of rifampicin associated to isoniazid and pyrazinamide (RHZ). It shows Brazil was one of the world’s first countries to use the RHZ regimen within a treatment system, with a first line regimen, another one specific for meningo-encephalic forms, for re-treatment of recurrences or of patients who returned with active tuberculosis after abandoning treatment, and a reserve regimen. The system was applied nationwide with guaranteed cost-free provision of medication, and self-administered. The author evaluates the growth of drug resistance, the emergence of multidrug-resistance and how management of this form of the disease has been organised

Entanglement evolution in finite dimensions

We provide a relation which describes how the entanglement of two d-level systems evolves as either system undergoes an arbitrary physical process. The dynamics of the entanglement turns out to be of a simple form, and is fully captured by a single quantity.Comment: 4 pages, 1 figure; new title and introduction, added references, some makeup; published versio