5,375 research outputs found
Effect of ancilla's structure on quantum error correction using the 7-qubit Calderbank-Shor-Steane code
In this work we discuss the ability of different types of ancillas to control
the decoherence of a qubit interacting with an environment. The error is
introduced into the numerical simulation via a depolarizing isotropic channel.
After the correction we calculate the fidelity as a quality criterion for the
qubit recovered. We observe that a recovery method with a three-qubit ancilla
provides reasonable good results bearing in mind its economy. If we want to go
further, we have to use fault-tolerant ancillas with a high degree of
parallelism, even if this condition implies introducing new ancilla
verification qubits.Comment: 24 pages, 10 Figures included. Accepted in Phys. Rev. A 200
Cambios del nivel del mar durante el Holoceno en el CantĂĄbrico a partir del estudio de la Turbera de TrengandĂn
[Resumen] El estudio de dos depĂłsitos proporcionan nuevos datos acerca de los cambios del nivel del mar durante el Holoceno. De acuerdo con ellos, durante el Sub-Boreal el nivel del mar no estuvo por encima de -2 m con respecto al nivel actual. El anĂĄlisis sugiere que el nivel del mar ascendiĂł gradualmente desde los -50 m al inicio del Holoceno, y no hay evidencias que sustenten la existencia de un nivel del mar mĂĄs alto que el actual, al menos hasta el Sub-AtlĂĄntico.[Abstract] The study of two deposits provides new data about sea level changes in the bay of Biscay during the Holocene. According to these data, the sea level was not above -2 m respect to present level during Sub-Boreal periodo The analysis suggests that sea level rose gradually from - 50 m at the beginning of the Holocene, and there is not evidence that support a level higher than present at least until Sub-Atlanti
Military service and crime: new evidence
BACKGROUND: Evidence indicates that a substantial proportion of military personnel are involved in high-risk and antisocial behaviors that place them at jeopardy for criminal justice system involvement. However, prior research on military service and crime has disproportionately focused on veterans from the Vietnam War era (1955â1975), and has tended to focus on either current or former military members.
METHODS: This study employed data from a population-based study (i.e., National Study on Drug Use and Health [NSDUH] between 2002 and 2014). It systematically examines the prevalence of self-reported antisocial behaviors, criminal justice system involvement, and substance abuse among the US civilian population and military service members, including reservists (nâ=â2206) and those who reported having been separated or retired from military service (nâ=â20,551). These factors are further examined across the developmental spectrum of adulthood (ages 18â34, 35â49, and 50â64).
RESULTS: Results showed that military members were more prone to lifetime arrests and overall substance misuse. However, additional findings emerged suggesting that, while the military population overall seems to be positively associated with higher criminal activity than that found in the civilian population, these findings were based on a specific subgroup of the veteran population. This subgroup is comprised of individuals who likely did not fit in with the military culture and were discharged from the military early in their careers.
CONCLUSION: Additional research on identifying this subgroup of military members is encouraged to better concentrate on prevention and treatment measures
Non-unitary representations of the SU(2) algebra in the Dirac equation with a Coulomb potential
A novel realization of the classical SU(2) algebra is introduced for the
Dirac relativistic hydrogen atom defining a set of operators that, besides,
allow the factorization of the problem. An extra phase is needed as a new
variable in order to define the algebra. We take advantage of the operators to
solve the Dirac equation using algebraic methods. To acomplish this, a similar
path to the one used in the angular momentum case is employed; hence, the
radial eigenfuntions calculated comprise non unitary representations of the
algebra. One of the interesting properties of such non unitary representations
is that they are not labeled by integer nor by half-integer numbers as happens
in the usual angular momentum representation.Comment: 20 pages 1 eps figure in a single zipped file, submitted to J. Math.
Phy
Hawking radiation by Kerr black holes and conformal symmetry
The exponential blueshift associated with the event horizon of a black hole
makes conformal symmetry play a fundamental role in accounting for its thermal
properties. Using a derivation based on two-point functions, we show that the
spectrum of thermal radiation of scalar particles by Kerr (and Schwarzschild)
black holes can be explicitly derived on the basis of a -dimensional
conformal symmetry arising in the wave equation near the horizon. This result
reinforces the recently conjectured relation between Kerr geometry and a
-dimensional conformal field theory.Comment: Version published in Phys. Rev. Let
Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics
The superposition principle is a very basic ingredient of quantum theory.
What may come as a surprise to many students, and even to many practitioners of
the quantum craft, is tha superposition has limitations imposed by certain
requirements of the theory. The discussion of such limitations arising from the
so-called superselection rules is the main purpose of this paper. Some of their
principal consequences are also discussed. The univalence, mass and particle
number superselection rules of non-relativistic quantum mechanics are also
derived using rather simple methods.Comment: 22 pages, no figure
- âŠ