3,349 research outputs found
Generalization of short coherent control pulses: extension to arbitrary rotations
We generalize the problem of the coherent control of small quantum systems to
the case where the quantum bit (qubit) is subject to a fully general rotation.
Following the ideas developed in Pasini et al (2008 Phys. Rev. A 77, 032315),
the systematic expansion in the shortness of the pulse is extended to the case
where the pulse acts on the qubit as a general rotation around an axis of
rotation varying in time. The leading and the next-leading corrections are
computed. For certain pulses we prove that the general rotation does not
improve on the simpler rotation with fixed axis.Comment: 6 pages, no figures; published versio
Symmetry-Enhanced Performance of Dynamical Decoupling
We consider a system with general decoherence and a quadratic dynamical
decoupling sequence (QDD) for the coherence control of a qubit coupled to a
bath of spins. We investigate the influence of the geometry and of the initial
conditions of the bath on the performance of the sequence. The overall
performance is quantified by a distance norm . It is expected that
scales with , the total duration of the sequence, as , where and are the number of pulses of the outer
and of the inner sequence, respectively. We show both numerically and
analytically that the state of the bath can boost the performance of QDD under
certain conditions: The scaling of QDD for a given number of pulses can be
enhanced by a factor of 2 if the bath is prepared in a highly symmetric state
and if the system Hamiltonian is SU(2) invariant.Comment: 9 pages, 4 figures, published versio
Pasta-making properties of the new durum wheat variety biensur suitable for the northern mediterranean environment
Industrial pasta is commonly made from mixtures of semolina from different durum wheat varieties, and there is a very low market presence of mono-varietal pasta from local, short supply chains. In this work, dough rheological properties and pasta quality traits of the new durum wheat cv. Biensur, which has a high HMW/LMW-GS ratio, were evaluated with a view to developing short-chain, mono-varietal pasta production in NE Italy. Chemical and sensory analyses on short-cut pasta, viz. tubetti, made with semolina from cv. Biensur at two drying temperatures revealed that it has good technological characteristics and stability, excellent cooking and sensory properties, and is comparable to the high-quality commercial reference cv. Aureo. We conclude that Biensur provides farmers and traders with new market opportunities and offers improvements to the environmental and economic sustainability of the durum wheat chain
Efficient Coherent Control by Optimized Sequences of Pulses of Finite Duration
Reliable long-time storage of arbitrary quantum states is a key element for
quantum information processing. In order to dynamically decouple a spin or
quantum bit from a dephasing environment, we introduce an optimized sequence of
control pulses of finite durations \tau\pp and finite amplitudes. The
properties of this sequence of length stem from a mathematically rigorous
derivation. Corrections occur only in order and \tau\pp^3 without
mixed terms such as T^N\tau\pp or T^N\tau\pp^2. Based on existing
experiments, a concrete setup for the verification of the properties of the
advocated realistic sequence is proposed.Comment: 8 pages, 1 figur
The effect of time-jitter in equispaced sampling wattmeters
This paper evaluates the effect of time-jitters in the equally spaced sampling wattmeters on the hypothesis of jitters uncorrelated with the input signals. The general case of two distinct time-jitters is considered, one common to the two channels and the other different for each one of them. The performance of the wattmeter has been evaluated by considering the asymptotic statistic parameters of the output. It has been shown that the different time-jitters introduce a bias and that both time-jitters contribute to the variance of the output. In any case, time-jitters introduce further bandwidth limitations which must be taken into account in the wattmeter accuracy evaluation. The theoretical results have been compared with simulated and experimental findings. Experimental results were obtained with a prototype in which both common and different time-jitters were separately added to the equally spaced sampling instants of the two input channels. In both cases, all the results were in good agreement with theoretical expectation
Optimization of Short Coherent Control Pulses
The coherent control of small quantum system is considered. For a two-level
system coupled to an arbitrary bath we consider a pulse of finite duration. We
derive the leading and the next-leading order corrections to the evolution
operator due to the non-commutation of the pulse and the bath Hamiltonian. The
conditions are computed that make the leading corrections vanish. The pulse
shapes optimized in this way are given for and pulses.Comment: 9 pages, 6 figures; published versio
Performance function for time-jittered equispaced sampling wattmeters
This paper evaluates the effect of time-jitter in the equally spaced sampling wattmeters on the hypothesis of equal effects in the two channels and a jitter uncorrelated with the input signals. It is shown that time-jitter, which is a random fluctuation with respect to the nominal sampling time, introduces a frequency limitation which is evaluated together with that due to the sampling strategy and filtering algorithm. The theoretical results are compared with the simulated one
Using earthworms as bioindicators of quality in no-till systems.
No Brasil, o plantio direto é o sistema de manejo do solo mais praticado. Dentre os diversos benefícios, o plantio direto promove as funções dos organismos, especialmente as minhocas, sobre a fertilidade do solo. Portanto, o presente estudo teve como objetivo avaliar as populações de minhocas, visando uma classificação da densidade e diversidade de minhocas em áreas sob plantio direto. As coletadas foram realizadas em fevereiro/março de 2010 e 2011, num total de 34 e 25 propriedades respectivamente em seis municípios da Bacia do Paraná 3, parte da bacia do lago de Itaipu. As minhocas foram amostradas no final da estação chuvosa, utilizando uma adaptação do Método para Biologia e Fertilidade em Solos Tropicais (TSBF), consistindo na coleta de 5 monolitos de 20 x 20 por 20 cm de profundidade, espaçados por mínimo 20 m um do outro, em um transecto linear. Foi realizada triagem manual no campo e as minhocas foram estocadas em sacos plásticos contendo solução de formaldeído 5%. As minhocas foram contadas e identificadas em nível de família, gênero e espécies. A simplificação da metodologia de amostragem objetivou possibilitar que os próprios agricultores avaliem as populações de minhocas em suas propriedades. A abundância de minhocas variou de 5 a 600 ind m-2 e 5 a 1150 ind m-2, respectivamente nas épocas de coletas em 2010 e 2011, enquanto o número de espécies variou de uma a seis em 2010 e de uma a sete em 2011 nas áreas sob plantio direto. Baseado neste estudo e em resultados de outros estudos anteriores, uma classificação para abundância e diversidade de minhocas em áreas sob plantio direto é proposta aqui, para Latossolos Vermelhos e regiões de clima quente do Paraná (Cfa Koeppen) : pobre >25 ind m-2 and 1 sp.; moderado ? 25 to 6 sp.Disponível online
Hidden order in bosonic gases confined in one dimensional optical lattices
We analyze the effective Hamiltonian arising from a suitable power series
expansion of the overlap integrals of Wannier functions for confined bosonic
atoms in a 1d optical lattice. For certain constraints between the coupling
constants, we construct an explicit relation between such an effective bosonic
Hamiltonian and the integrable spin- anisotropic Heisenberg model. Therefore
the former results to be integrable by construction. The field theory is
governed by an anisotropic non linear -model with singlet and triplet
massive excitations; such a result holds also in the generic non-integrable
cases. The criticality of the bosonic system is investigated. The schematic
phase diagram is drawn. Our study is shedding light on the hidden symmetry of
the Haldane type for one dimensional bosons.Comment: 5 pages; 1 eps figure. Revised version, to be published in New. J.
Phy
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