23,357 research outputs found
Security of two-way quantum cryptography against asymmetric Gaussian attacks
Recently, we have shown the advantages of two-way quantum communications in
continuous variable quantum cryptography. Thanks to this new approach, two
honest users can achieve a non-trivial security enhancement as long as the
Gaussian interactions of an eavesdropper are independent and identical. In this
work, we consider asymmetric strategies where the Gaussian interactions can be
different and classically correlated. For several attacks of this kind, we
prove that the enhancement of security still holds when the two-way protocols
are used in direct reconciliation.Comment: Proceeding of the SPIE Conference "Quantum Communications and Quantum
Imaging VI" - San Diego 2008. This paper is connected with
arXiv:quant-ph/0611167 (for the last version see: Nature Physics 4, 726
(2008)
Confidential direct communications: a quantum approach using continuous variables
We consider the problem of privacy in direct communications, showing how
quantum mechanics can be useful to guarantee a certain level of
confidentiality. In particular, we review a continuous variable approach
recently proposed by us [S. Pirandola et al., Europhys. Lett. 84, 20013
(2008)]. Here, we analyze the degree of privacy of this technique against a
broader class of attacks, which includes non-Gaussian eavesdropping.Comment: Invited paper. Extension of results presented in arXiv:0802.0656
(REVTeX, 11 pages, 11 figures
Effects of non-pharmacological or pharmacological interventions on cognition and brain plasticity of aging individuals.
Brain aging and aging-related neurodegenerative disorders are major health challenges faced by modern societies. Brain aging is associated with cognitive and functional decline and represents the favourable background for the onset and development of dementia. Brain aging is associated with early and subtle anatomo-functional physiological changes that often precede the appearance of clinical signs of cognitive decline. Neuroimaging approaches unveiled the functional correlates of these alterations and helped in the identification of therapeutic targets that can be potentially useful in counteracting age-dependent cognitive decline. A growing body of evidence supports the notion that cognitive stimulation and aerobic training can preserve and enhance operational skills in elderly individuals as well as reduce the incidence of dementia. This review aims at providing an extensive and critical overview of the most recent data that support the efficacy of non-pharmacological and pharmacological interventions aimed at enhancing cognition and brain plasticity in healthy elderly individuals as well as delaying the cognitive decline associated with dementia
On the Evolution, Numbers, and Characteristics of Close-Binary Supersoft Sources
The ability to perform detailed evolutionary calculations is essential to the
development of a well-defined and testable binary model. Unfortunately,
traditional evolutionary calculations cannot be used to follow a significant
fraction of possible close-binary supersoft sources (CBSSs). It is therefore
important to examine the input physics carefully, to be sure that all relevant
and potentially important physical processes are included. In this paper we
continue a line of research begun last year, and explore the role that winds
are expected to play in the evolution of CBSSs. We find that at least a subset
of the systems that seemed to be candidates for common envelope evolution may
survive, if radiation emitted by white dwarf drives winds from the system. We
study the effects of winds on the binary evolution of CBSSs, and compute the
number and characteristics of CBSSs expected to be presently active in galaxies
such as our own or M31.Comment: 13 pages; figures included in 0.33 M postscript file; in Supersoft
X-ray Sources, ed. J. Greiner (Springer-Verlag: Berlin) (1996
Minimal qudit code for a qubit in the phase-damping channel
Using the stabilizer formalism we construct the minimal code into a
D-dimensional Hilbert space (qudit) to protect a qubit against phase damping.
The effectiveness of this code is then studied by means of input-output
fidelity.Comment: 9 pages, 3 figures. REVTe
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