110 research outputs found
Notes on entropic characteristics of quantum channels
One of most important issues in quantum information theory concerns
transmission of information through noisy quantum channels. We discuss few
channel characteristics expressed by means of generalized entropies. Such
characteristics can often be dealt in line with more usual treatment based on
the von Neumann entropies. For any channel, we show that the -average output
entropy of degree is bounded from above by the -entropy of the
input density matrix. Concavity properties of the -entropy exchange are
considered. Fano type quantum bounds on the -entropy exchange are
derived. We also give upper bounds on the map -entropies in terms of the
output entropy, corresponding to the completely mixed input.Comment: 10 pages, no figures. The statement of Proposition 1 is explicitly
illustrated with the depolarizing channel. The bibliography is extended and
updated. More explanations. To be published in Cent. Eur. J. Phy
Origin and Properties of the Gap in the Half-Ferromagnetic Heusler Alloys
We study the origin of the gap and the role of chemical composition in the
half-ferromagnetic Heusler alloys using the full-potential screened KKR method.
In the paramagnetic phase the C1_b compounds, like NiMnSb, present a gap.
Systems with 18 valence electrons, Z_t, per unit cell, like CoTiSb, are
semiconductors, but when Z_t > 18 antibonding states are also populated, thus
the paramagnetic phase becomes unstable and the half-ferromagnetic one is
stabilized. The minority occupied bands accommodate a total of nine electrons
and the total magnetic moment per unit cell in mu_B is just the difference
between Z_t and . While the substitution of the transition metal
atoms may preserve the half-ferromagnetic character, substituting the atom
results in a practically rigid shift of the bands and the loss of
half-metallicity. Finally we show that expanding or contracting the lattice
parameter by 2% preserves the minority-spin gap.Comment: 11 pages, 7 figures New figures, revised tex
Seismic analysis of four solar-like stars observed during more than eight months by <i>Kepler</i>
Differences in overland flow, hydrophobicity and soil moisture dynamics between Mediterranean woodland types in a peri-urban catchment in Portugal
Ruminal parameters of bovines fed diets based on sugar cane with doses of calcium hydroxide
Valuation of the Aroeira (Myracrodruon urundeuva Allemão): perspectives on conservation
Classes de perfilhos na composição do índice de área foliar em pastos de capim-elefante
Antimicrobial activity of copaíba (Copaifera langsdorffii) oleoresin on bacteria of clinical significance in cutaneous wounds
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