381 research outputs found
Theory of Single Electron Spin Relaxation in Si/SiGe Lateral Coupled Quantum Dots
We investigate the spin relaxation induced by acoustic phonons in the
presence of spin-orbit interactions in single electron Si/SiGe lateral coupled
quantum dots. The relaxation rates are computed numerically in single and
double quantum dots, in in-plane and perpendicular magnetic fields. The
deformation potential of acoustic phonons is taken into account for both
transverse and longitudinal polarizations and their contributions to the total
relaxation rate are discussed with respect to the dilatation and shear
potential constants. We find that in single dots the spin relaxation rate
scales approximately with the seventh power of the magnetic field, in line with
a recent experiment. In double dots the relaxation rate is much more sensitive
to the dot spectrum structure, as it is often dominated by a spin hot spot. The
anisotropy of the spin-orbit interactions gives rise to easy passages, special
directions of the magnetic field for which the relaxation is strongly
suppressed. Quantitatively, the spin relaxation rates in Si are typically 2
orders of magnitude smaller than in GaAs due to the absence of the
piezoelectric phonon potential and generally weaker spin-orbit interactions.Comment: 10 pages, 9 figure
Theory of Spin Relaxation in Two-Electron Lateral Coupled Quantum Dots
A global quantitative picture of the phonon-induced two-electron spin
relaxation in GaAs double quantum dots is presented using highly accurate
numerical calculations. Wide regimes of interdot coupling, magnetic field
magnitude and orientation, and detuning are explored in the presence of a
nuclear bath. Most important, the unusually strong magnetic anisotropy of the
singlet-triplet relaxation can be controlled by detuning switching the
principal anisotropy axes: a protected state becomes unprotected upon detuning,
and vice versa. It is also established that nuclear spins can dominate spin
relaxation for unpolarized triplets even at high magnetic fields, contrary to
common belief. These findings are central to designing quantum dots geometries
for spin-based quantum information processing with minimal environmental
impact.Comment: 8 pages, 8 figure
Theory of Spin Relaxation in Two-Electron Lateral Coupled Si/SiGe Quantum Dots
Highly accurate numerical results of phonon-induced two-electron spin
relaxation in silicon double quantum dots are presented. The relaxation,
enabled by spin-orbit coupling and the nuclei of Si (natural or purified
abundance), are investigated for experimentally relevant parameters, the
interdot coupling, the magnetic field magnitude and orientation, and the
detuning. We calculate relaxation rates for zero and finite temperatures (100
mK), concluding that our findings for zero temperature remain qualitatively
valid also for 100 mK. We confirm the same anisotropic switch of the axis of
prolonged spin lifetime with varying detuning as recently predicted in GaAs.
Conditions for possibly hyperfine-dominated relaxation are much more stringent
in Si than in GaAs. For experimentally relevant regimes, the spin-orbit
coupling, although weak, is the dominant contribution, yielding anisotropic
relaxation rates of at least two order of magnitude lower than in GaAs.Comment: 11 pages, 10 figure
Lorentz meets Fano spectral line shapes: A universal phase and its laser control
Symmetric Lorentzian and asymmetric Fano line shapes are fundamental
spectroscopic signatures that quantify the structural and dynamical properties
of nuclei, atoms, molecules, and solids. This study introduces a universal
temporal-phase formalism, mapping the Fano asymmetry parameter q to a phase
{\phi} of the time-dependent dipole-response function. The formalism is
confirmed experimentally by laser-transforming Fano absorption lines of
autoionizing helium into Lorentzian lines after attosecond-pulsed excitation.
We also prove the inverse, the transformation of a naturally Lorentzian line
into a Fano profile. A further application of this formalism amplifies
resonantly interacting extreme-ultraviolet light by quantum-phase control. The
quantum phase of excited states and its response to interactions can thus be
extracted from line-shape analysis, with scientific applications in many
branches of spectroscopy.Comment: 11 pages, 4 figure
1985 Chogoria Community Health Survey : report of principal findings, October 1987
During August 1985, the Community Health Department of Chogoria Hospital in central Kenya carried out a survey of women of childbearing age throughout the area in which it provides services. This survey, the Chogoria Community Health Survey (CCHS), covered a variety of topics related to maternal and child health and the use of health services. It was designed to gauge various aspects of the health status and needs of the population in the catchment area and, thus, to suggest appropriate strategies and directions for future interventions. The survey also documents the current situation in an area that is reported to be one of the most successful in rural sub-Saharan Africa in regard to maternal and child health and family planning
Production of benzylisoquinoline alkaloids in Saccharomyces cerevisiae
The benzylisoquinoline alkaloids (BIAs) are a diverse class of metabolites that exhibit a broad range of pharmacological activities and are synthesized through plant biosynthetic pathways comprised of complex enzyme activities and regulatory strategies. We have engineered yeast to produce the key intermediate reticuline and downstream BIA metabolites from a commercially available substrate. An enzyme tuning strategy was implemented that identified activity differences between variants from different plants and determined optimal expression levels. By synthesizing both stereoisomer forms of reticuline and integrating enzyme activities from three plant sources and humans, we demonstrated the synthesis of metabolites in the sanguinarine/berberine and morphinan branches. We also demonstrated that a human P450 enzyme exhibits a novel activity in the conversion of (R)-reticuline to the morphinan alkaloid salutaridine. Our engineered microbial hosts offer access to a rich group of BIA molecules and associated activities that will be further expanded through synthetic chemistry and biology approaches
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
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