4,540 research outputs found
Simultaneous Spin-Charge Relaxation in Double Quantum Dots
We investigate phonon-induced spin and charge relaxation mediated by
spin-orbit and hyperfine interactions for a single electron confined within a
double quantum dot. A simple toy model incorporating both direct decay to the
ground state of the double dot and indirect decay via an intermediate excited
state yields an electron spin relaxation rate that varies non-monotonically
with the detuning between the dots. We confirm this model with experiments
performed on a GaAs double dot, demonstrating that the relaxation rate exhibits
the expected detuning dependence and can be electrically tuned over several
orders of magnitude. Our analysis suggests that spin-orbit mediated relaxation
via phonons serves as the dominant mechanism through which the double-dot
electron spin-flip rate varies with detuning.Comment: 5 pages, 3 figures, Supplemental Material (2 pages, 2 figures
Bone mineral content in Hawaiian, Asian, and Filipino children.
Os calcis bone mineral content (BMC) was measured by single photon absorptiometry in 86 children, ages 6 to 13 years from Hawaiian, Oriental, Caucasian, and Filipino ethnic groups. Pearson correlations indicated significant positive correlations between BMC and age, height, and weight. However, there were no significant differences in age, height or weight between ethnic groups. ANOVA revealed a significant effect of ethnic group on BMC with the Hawaiian group having a significantly higher BMC than the Asian or Caucasian groups. When age, height and weight were controlled for, ANCOVA still showed a significant effect of ethnicity on BMC. The current findings suggest that ethnic differences can develop early in life
Universal phase shift and non-exponential decay of driven single-spin oscillations
We study, both theoretically and experimentally, driven Rabi oscillations of
a single electron spin coupled to a nuclear spin bath. Due to the long
correlation time of the bath, two unusual features are observed in the
oscillations. The decay follows a power law, and the oscillations are shifted
in phase by a universal value of ~pi/4. These properties are well understood
from a theoretical expression that we derive here in the static limit for the
nuclear bath. This improved understanding of the coupled electron-nuclear
system is important for future experiments using the electron spin as a qubit.Comment: Main text: 4 pages, 3 figures, Supplementary material: 2 pages, 3
figure
Spin-echo of a single electron spin in a quantum dot
We report a measurement of the spin-echo decay of a single electron spin
confined in a semiconductor quantum dot. When we tip the spin in the transverse
plane via a magnetic field burst, it dephases in 37 ns due to the Larmor
precession around a random effective field from the nuclear spins in the host
material. We reverse this dephasing to a large extent via a spin-echo pulse,
and find a spin-echo decay time of about 0.5 microseconds at 70 mT. These
results are in the range of theoretical predictions of the electron spin
coherence time governed by the dynamics of the electron-nuclear system.Comment: 5 pages, 4 figure
Detection of single electron spin resonance in a double quantum dot
Spin-dependent transport measurements through a double quantum dot are a
valuable tool for detecting both the coherent evolution of the spin state of a
single electron as well as the hybridization of two-electron spin states. In
this paper, we discuss a model that describes the transport cycle in this
regime, including the effects of an oscillating magnetic field (causing
electron spin resonance) and the effective nuclear fields on the spin states in
the two dots. We numerically calculate the current flow due to the induced spin
flips via electron spin resonance and we study the detector efficiency for a
range of parameters. The experimental data are compared with the model and we
find a reasonable agreement.Comment: 7 pages, 5 figures. To be published in Journal of Applied Physics,
proceedings ICPS 200
CMS Software Distribution on the LCG and OSG Grids
The efficient exploitation of worldwide distributed storage and computing
resources available in the grids require a robust, transparent and fast
deployment of experiment specific software. The approach followed by the CMS
experiment at CERN in order to enable Monte-Carlo simulations, data analysis
and software development in an international collaboration is presented. The
current status and future improvement plans are described.Comment: 4 pages, 1 figure, latex with hyperref
Nuclear Spin Effects in Semiconductor Quantum Dots
The interaction of an electronic spin with its nuclear environment, an issue known as the central spin problem, has been the subject of considerable attention due to its relevance for spin-based quantum computation using semiconductor quantum dots. Independent control of the nuclear spin bath using nuclear magnetic resonance techniques and dynamic nuclear polarization using the central spin itself offer unique possibilities for manipulating the nuclear bath with significant consequences for the coherence and controlled manipulation of the central spin. Here we review some of the recent optical and transport experiments that have explored this central spin problem using semiconductor quantum dots. We focus on the interaction between nuclear spins and a spin of a single electron or valence-band hole. We also review the experimental techniques as well as the key theoretical ideas and the implications for quantum information science.Physic
Multiple Nuclear Polarization States in a Double Quantum Dot
We observe multiple stable states of nuclear polarization in a double quantum
dot under conditions of electron spin resonance. The stable states can be
understood within an elaborated theoretical rate equation model for the
polarization in each of the dots, in the limit of strong driving. This model
also captures unusual features of the data, such as fast switching and a
`wrong' sign of polarization. The results reported enable applications of this
polarization effect, including manipulation and control of nuclear fields.Comment: 5 pages, 4 figures, 7 pages supplementary materia
Resolving Spin-Orbit and Hyperfine Mediated Electric Dipole Spin Resonance in a Quantum Dot
We investigate the electric manipulation of a single electron spin in a
single gate-defined quantum dot. We observe that so-far neglected differences
between the hyperfine and spin-orbit mediated electric dipole spin resonance
conditions have important consequences at high magnetic fields. In experiments
using adiabatic rapid passage to invert the electron spin, we observe an
unusually wide and asymmetric response as a function of magnetic field.
Simulations support the interpretation of the lineshape in terms of four
different resonance conditions. These findings may lead to isotope-selective
control of dynamic nuclear polarization in quantum dots
Investigation of small-scale processes in the rhizosphere of Lupinus albus using micro push-pull tests
Background and Aims: Rhizosphere processes affect the mobility, phytoavailability and toxicity of solutes in soil. To study reactions in the rhizosphere under quasi in situ conditions, we recently developed the "micro push-pull test” (μPPT) method, combining micro-suction cups with the principle of the "push-pull test” method known from groundwater applications. Here we report the application of μPPT to investigate rhizosphere reactions in situ, i.e. degradation of deuterated citrate (citrate-d4) in the rhizosphere of Lupinus albus grown in sand-filled rhizoboxes. Methods: In a μPPT, a solution containing reactive (citrate-d4) and non-reactive solutes (bromide) is injected into a porous medium and shortly thereafter, the pore water solution is re-extracted from the same location. Concentration ("breakthrough”) curves of extracted reactants can be compared to those of the non-reactive solute, allowing the determination of reaction rates. We applied the μPPT in rhizoboxes with Lupinus albus and sampled different types of micro-habitats: bulk soil, rhizosphere of normal roots and rhizosphere of cluster roots of different ages. Results: Breakthrough curves of citrate-d4 varied considerably between tests adjacent to cluster roots and normal roots, and in bulk soil. Degradation of citrate-d4 in bulk soil and adjacent to normal roots was below detection, while we found strong degradation of citrate-d4 adjacent to 4 to 5-days old cluster roots. In situ degradation rate constants for citrate-d4 around cluster roots were found to be in the range from 0.38 to 0.71h−1. Conclusions: We successfully applied the μPPT to the rhizosphere. The μPPT is useful to investigate local processes in microcosms and to monitor processes also over time (e.g., during cluster-root development) due to its non-destructive nature
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