13,691 research outputs found
Unusual behaviours and Impurity Effects in the Noncentrosymmetric Superconductor CePt3Si
We report a study in which the effect of defects/impurities, growth process,
off-stoichiometry, and presence of impurity phases on the superconducting
properties of noncentrosymmetric CePt3Si is analysed by means of the
temperature dependence of the magnetic penetration depth. We found that the
linear low-temperature response of the penetration depth -indicative of line
nodes in this material- is robust regarding sample quality, in contrast to what
is observed in unconventional centrosymmetric superconductors with line nodes.
We discuss evidence that the broadness of the superconducting transition may be
intrinsic, though not implying the existence of a second superconducting
transition. The superconducting transition temperature systematically occurs
around 0.75 K in our measurements, in agreement with resistivity and ac
magnetic susceptibility data but in conflict with specific heat, thermal
conductivity and NMR data in which Tc is about 0.5 K. Random defects do not
change the linear low-temperature dependence of the penetration depth in the
heavy-fermion CePt3Si with line nodes, as they do in unconventional
centrosymmetric superconductors with line nodes.Comment: To appear in New Journal of Physic
Experimental investigation of quantum key distribution with position and momentum of photon pairs
We investigate the utility of Einstein-Podolsky-Rosen correlations of the
position and momentum of photon pairs from parametric down-conversion in the
implementation of a secure quantum key distribution protocol. We show that
security is guaranteed by the entanglement between downconverted pairs, and can
be checked by either direct comparison of Alice and Bob's measurement results
or evaluation of an inequality of the sort proposed by Mancini et al. (Phys.
Rev. Lett. 88, 120401 (2002)).Comment: 6 pages, 6 figures, subimitted for publicatio
Identificação e controle das principais pragas em pomares de citros no Pará.
Publicado também como folder (FD 00715).bitstream/item/28007/1/com.tec.119.pdfDisponível também on-line
Cornops frenatum frenatum (Marschall) (Orthoptera: Acrididae): principal desfolhador em cultivos de heliconia spp. (Heliconiaceae) no Estado do Pará.
bitstream/item/27882/1/Com.tec.164.pd
Synthesis and characterization of nanostrctured V2O5nH2O prepared throughout the hydrothermal method.
Frustration and sound attenuation in structural glasses
Three classes of harmonic disorder systems (Lennard-Jones like glasses,
percolators above threshold, and spring disordered lattices) have been
numerically investigated in order to clarify the effect of different types of
disorder on the mechanism of high frequency sound attenuation. We introduce the
concept of frustration in structural glasses as a measure of the internal
stress, and find a strong correlation between the degree of frustration and the
exponent alpha that characterizes the momentum dependence of the sound
attenuation . In particular, alpha decreases from
about d+1 in low-frustration systems (where d is the spectral dimension), to
about 2 for high frustration systems like the realistic glasses examined.Comment: Revtex, 4 pages including 4 figure
Quantum key distribution with higher-order alphabets using spatially-encoded qudits
We propose and demonstrate a quantum key distribution scheme in higher-order
-dimensional alphabets using spatial degrees of freedom of photons. Our
implementation allows for the transmission of 4.56 bits per sifted photon,
while providing improved security: an intercept-resend attack on all photons
would induce an error rate of 0.47. Using our system, it should be possible to
send more than a byte of information per sifted photon.Comment: 4 pages, 5 figures. Replaced with published versio
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