579 research outputs found
Models of environment and T_1 relaxation in Josephson Charge Qubits
A theoretical interpretation of the recent experiments of Astafiev et. al. on
the T_1-relaxation rate in Josephson Charge Qubits is proposed. The
experimentally observed reproducible nonmonotonic dependence of T_1 on the
splitting E_J of the qubit levels suggests further specification of the
previously proposed models of the background charge noise. From our point of
view the most promising is the ``Andreev fluctuator'' model of the noise. In
this model the fluctuator is a Cooper pair that tunnels from a superconductor
and occupies a pair of localized electronic states. Within this model one can
naturally explain both the average linear T_1(E_J) dependence and the irregular
fluctuations. The role of fluctuators in the formation of strong resonant peaks
in this dependence is also discussed.Comment: 4 pages, 3 figure
Magnetism in SQUIDs at Millikelvin Temperatures
We have characterized the temperature dependence of the flux threading dc
SQUIDs cooled to millikelvin temperatures. The flux increases as 1/T as
temperature is lowered; moreover, the flux change is proportional to the
density of trapped vortices. The data is compatible with the thermal
polarization of surface spins in the trapped fields of the vortices. In the
absence of trapped flux, we observe evidence of spin-glass freezing at low
temperature. These results suggest an explanation for the "universal" 1/f flux
noise in SQUIDs and superconducting qubits.Comment: 4 pages, 4 figure
Exact solution for the dynamical decoupling of a qubit with telegraph noise
We study the dissipative dynamics of a qubit that is afflicted by classical
random telegraph noise and it is subject to dynamical decoupling. We derive
exact formulas for the qubit dynamics at arbitrary working points in the limit
of infinitely strong control pulses (bang-bang control) and we investigate in
great detail the efficiency of the dynamical decoupling techniques both for
Gaussian and non-Gaussian (slow) noise at qubit pure dephasing and at optimal
point. We demonstrate that control sequences can be successfully implemented as
diagnostic tools to infer spectral proprieties of a few fluctuators interacting
with the qubit. The analysis is extended in order to include the effect of
noise in the pulses and we give upper bounds on the noise levels that can be
tolerated in the pulses while still achieving efficient dynamical decoupling
performance
Entanglement detection for electrons via witness operators
We discuss an implementation of the entanglement witness, a method to detect
entanglement with few local measurements, in systems where entangled electrons
are generated both in the spin and orbital degrees of freedom.
We address the efficiency of this method in various setups, including two
different particle-hole entanglement structures, and we demonstrate that it can
also be used to infer information on the possible dephasing afflicting the
devices.Comment: 12 pages, 5 figures; published versio
Non-Abelian phases, charge pumping, and quantum computation with Josephson junctions
Non-Abelian geometric phases can be generated and detected in certain
superconducting nanocircuits. Here we consider an example where the holonomies
are related to the adiabatic charge dynamics of the Josephson network. We
demonstrate that such a device can be applied both for adiabatic charge pumping
and as an implementation of a quantum computer.Comment: 11 pages RevTex, 3 figures in eps format, revised versio
The product of the rice myb7 unspliced mRNA dimerizes with the maize leucine-zipper opaque2 and stimulates its activity in transient expression assay
myb7 mRNA is present in rice in spliced and unspliced forms, splicing being enhanced by anoxia. The protein (Mybleu) encoded by the unspliced mRNA is composed of an incomplete Myb domain followed by a leucine zipper; however, it lacks canonical sequences for DNA binding, transcriptional activation, and nuclear localization. We show here that in transiently transformed tobacco protoplasts, Mybleu is able to enhance the transcriptional activity of the maize leucine zipper Opaque2 on its target b32 promoter. The Mybleu transactivation effect is strictly dependent on the presence of Opaque2 and is driven by Mybleu-Opaque2 heterodimers. Mybleu is located in the nucleus, both in rice and in transformed tobacco protoplasts. In rice, the protein is expressed in regions corresponding to undifferentiated cells of roots and coleoptiles. Therefore, myb7 mRNA encodes, depending on its splicing, two transcription factors belonging to separate classes. One of them, Myblue, has novel structural characteristics, suggesting the existence of new mechanisms acting in the activation of transcription.
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Structured environments in solid state systems: crossover from Gaussian to non-Gaussian behavior
The variety of noise sources typical of the solid state represents the main
limitation toward the realization of controllable and reliable quantum
nanocircuits, as those allowing quantum computation. Such ``structured
environments'' are characterized by a non-monotonous noise spectrum sometimes
showing resonances at selected frequencies. Here we focus on a prototype
structured environment model: a two-state impurity linearly coupled to a
dissipative harmonic bath. We identify the time scale separating Gaussian and
non-Gaussian dynamical regimes of the Spin-Boson impurity. By using a
path-integral approach we show that a qubit interacting with such a structured
bath may probe the variety of environmental dynamical regimes.Comment: 8 pages, 9 figures. Proceedings of the DECONS '06 Conferenc
Construction of a synthetic infectious cDNA clone of Grapevine Algerian latent virus (GALV-Nf) and its biological activity in Nicotiana benthamiana and grapevine plants
Background: Grapevine Algerian latent virus (GALV) is a tombusvirus first isolated in 1989 from an Algerian grapevine (Vitis spp.) plant and more recently from water samples and commercial nipplefruit and statice plants. No further reports of natural GALV infections in grapevine have been published in the last two decades, and artificial inoculations of grapevine plants have not been reported. We developed and tested a synthetic GALV construct for the inoculation of Nicotiana benthamiana plants and different grapevine genotypes to investigate the ability of this virus to infect and spread systemically in different hosts. Methods: We carried out a phylogenetic analysis of all known GALV sequences and an epidemiological survey of grapevine samples to detect the virus. A GALV-Nf clone under the control of the T7 promoter was chemically synthesized based on the full-length sequence of the nipplefruit isolate GALV-Nf, the only available sequence at the time the project was conceived, and the infectious transcripts were tested in N. benthamiana plants. A GALV-Nf-based binary vector was then developed for the agroinoculation of N. benthamiana and grapevine plants. Infections were confirmed by serological and molecular analysis and the resulting ultrastructural changes were investigated in both species. Results: Sequence analysis showed that the GALV coat protein is highly conserved among diverse isolates. The first epidemiological survey of cDNAs collected from 152 grapevine plants with virus-like symptoms did not reveal the presence of GALV in any of the samples. The agroinoculation of N. benthamiana and grapevine plants with the GALV-Nf binary vector promoted efficient infections, as revealed by serological and molecular analysis. The GALV-Nf infection of grapevine plants was characterized in more detail by inoculating different cultivars, revealing distinct patterns of symptom development. Ultrastructural changes induced by GALV-Nf in N. benthamiana were similar to those induced by tombusviruses in other hosts, but the cytopathological alterations in grapevine plants were less severe. Conclusions: This is the first report describing the development of a synthetic GALV-Nf cDNA clone, its artificial transmission to grapevine plants and the resulting symptoms and cytopathological alterations
Marcadores moleculares para análise genética de germoplasma de pereira: uso na organização dos recursos genéticos e no melhoramento genético.
O objetivo deste estudo foi o de ajustar as metodologias cientÃficas para a obtenção de marcadores microssatélites e RAPD para análise genética do germoplasma conservado em coleções de pera, visando à organização dos recursos genéticos da espécie do Brasil e ao apoio de atividades de melhoramento genético.bitstream/item/73908/1/Circular-Tecnica-93-online.pd
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