203 research outputs found
Nuclear spin physics in quantum dots: an optical investigation
The mesoscopic spin system formed by the 10E4-10E6 nuclear spins in a
semiconductor quantum dot offers a unique setting for the study of many-body
spin physics in the condensed matter. The dynamics of this system and its
coupling to electron spins is fundamentally different from its bulk
counter-part as well as that of atoms due to increased fluctuations that result
from reduced dimensions. In recent years, the interest in studying quantum dot
nuclear spin systems and their coupling to confined electron spins has been
fueled by its direct implication for possible applications of such systems in
quantum information processing as well as by the fascinating nonlinear
(quantum-)dynamics of the coupled electron-nuclear spin system. In this
article, we review experimental work performed over the last decades in
studying this mesoscopic,coupled electron-nuclear spin system and discuss how
optical addressing of electron spins can be exploited to manipulate and
read-out quantum dot nuclei. We discuss how such techniques have been applied
in quantum dots to efficiently establish a non-zero mean nuclear spin
polarization and, most recently, were used to reduce fluctuations of the
average quantum dot nuclear spin orientation. Both results in turn have
important implications for the preservation of electron spin coherence in
quantum dots, which we discuss. We conclude by speculating how this recently
gained understanding of the quantum dot nuclear spin system could in the future
enable experimental observation of quantum-mechanical signatures or possible
collective behavior of mesoscopic nuclear spin ensembles.Comment: 61 pages, 45 figures, updated reference list, corrected typographical
error
Dynamic nuclear polarization of a single charge-tunable InAs/GaAs quantum dot
We report on the dynamic nuclear polarization of a single charge-tunable
self-assembled InAs/GaAs quantum dot in a longitudinal magnetic field of
0.2T. The hyperfine interaction between the optically oriented electron
and nuclei spins leads to the polarization of the quantum dot nuclei measured
by the Overhauser-shift of the singly-charged excitons ( and ).
When going from to , we observe a reversal of this shift which
reflects the average electron spin optically written down in the quantum dot
either in the state or in the final state of recombination. We
discuss a theoretical model which indicates an efficient depolarization
mechanism for the nuclei limiting their polarization to ~10%.Comment: 4+ pages, 3 figure
The forensiX evidence collection tube and its impact on DNA preservation and recovery
Biological samples are vulnerable to degradation from the time they are collected until they are analysed at the laboratory. Biological contaminants, such as bacteria, fungi, and enzymes, as well as environmental factors, such as sunlight, heat, and humidity, can increase the rate of DNA degradation. Currently, DNA samples are normally dried or frozen to limit their degradation prior to their arrival at the laboratory. In this study, the effect of the sample drying rate on DNA preservation was investigated, as well as a comparison between drying and freezing methods. The drying performances of two commercially available DNA collection tools (swab and drying tube) with different drying rates were evaluated. The swabs were used to collect human saliva, placed into the drying tubes, and stored in a controlled environment at 25°C and 60% relative humidity, or frozen at −20°C, for 2 weeks. Swabs that were stored in fast sample drying tubes yielded 95% recoverable DNA, whereas swabs stored in tubes with slower sample drying rates yielded only 12% recoverable DNA; saliva stored in a microtube at −20°C was used as a control. Thus, DNA sampling tools that offer rapid drying can significantly improve the preservation of DNA collected on a swab, increasing the quantity of DNA available for subsequent analysis
Hyperfine interaction in InAs/GaAs self-assembled quantum dots : dynamical nuclear polarization versus spin relaxation
We report on the influence of hyperfine interaction on the optical
orientation of singly charged excitons X+ and X- in self-assembled InAs/GaAs
quantum dots. All measurements were carried out on individual quantum dots
studied by micro-photoluminescence at low temperature. We show that the
hyperfine interaction leads to an effective partial spin relaxation, under
50kHz modulated excitation polarization, which becomes however strongly
inhibited under steady optical pumping conditions because of dynamical nuclear
polarization. This optically created magnetic-like nuclear field can become
very strong (up to ~4 T) when it is generated in the direction opposite to a
longitudinally applied field, and exhibits then a bistability regime. This
effect is very well described by a theoretical model derived in a perturbative
approach, which reveals the key role played by the energy cost of an electron
spin flip in the total magnetic field. Eventually, we emphasize the
similarities and differences between X+ and X- trions with respect to the
hyperfine interaction, which turn out to be in perfect agreement with the
theoretical description.Comment: 10 pages, 5 figure
Controlling the polarization eigenstate of a quantum dot exciton with light
We demonstrate optical control of the polarization eigenstates of a neutral
quantum dot exciton without any external fields. By varying the excitation
power of a circularly polarized laser in micro-photoluminescence experiments on
individual InGaAs quantum dots we control the magnitude and direction of an
effective internal magnetic field created via optical pumping of nuclear spins.
The adjustable nuclear magnetic field allows us to tune the linear and circular
polarization degree of the neutral exciton emission. The quantum dot can thus
act as a tunable light polarization converter.Comment: 5 pages, 3 figure
Standardized, systemic phenotypic analysis reveals kidney dysfunction as main alteration of Kctd1 I27N mutant mice
Background: Increased levels of blood plasma urea were used as phenotypic parameter for establishing novel mouse models for kidney diseases on the genetic background of C3H inbred mice in the phenotype-driven Munich ENU mouse mutagenesis project. The phenotypically dominant mutant line HST014 was established and further analyzed. Methods: Analysis of the causative mutation as well as the standardized, systemic phenotypic analysis of the mutant line was carried out. Results: The causative mutation was detected in the potassium channel tetramerization domain containing 1 (Kctd1) gene which leads to the amino acid exchange Kctd1 I27N thereby affecting the functional BTB domain of the protein. This line is the first mouse model harboring a Kctd1 mutation. Kctd1 I27N homozygous mutant mice die perinatally. Standardized, systemic phenotypic analysis of Kctd1 I27N heterozygous mutants was carried out in the German Mouse Clinic (GMC). Systematic morphological investigation of the external physical appearance did not detect the specific alterations that are described in KCTD1 mutant human patients affected by the scalp-ear-nipple (SEN) syndrome. The main pathological phenotype of the Kctd1 I27N heterozygous mutant mice consists of kidney dysfunction and secondary effects thereof, without gross additional primary alterations in the other phenotypic parameters analyzed. Genome-wide transcriptome profiling analysis at the age of 4 months revealed about 100 differentially expressed genes (DEGs) in kidneys of Kctd1 I27N heterozygous mutants as compared to wild-type controls. Conclusions: In summary, the main alteration of the Kctd1 I27N heterozygous mutants consists in kidney dysfunction. Additional analyses in 9–21 week-old heterozygous mutants revealed only few minor effects
Decreased levels of homoarginine and asymmetric dimethylarginine in children with type 1 diabetes: associations with cardiovascular risk factors but no effect by atorvastin
Objectives: To investigate homoarginine and asymmetric dimethylarginine (ADMA) in controls compared to children with type 1 diabetes (T1D) and if homoarginine and ADMA are affected by atorvastatin. Methods: Homoarginine and ADMA levels of 28 T1D patients were compared to levels of 41 controls. In T1D patients, homoarginine and ADMA were determined at baseline, 1 year, and 2 years at daily 10 mg atorvastatin or placebo within a double-blind study. Results: At baseline, both homoarginine and ADMA were lower (p<0.001) in T1D patients compared to controls. In T1D patients, homoarginine and ADMA were not influenced by atorvastatin. Inverse correlations between homoarginine and HbA1c (p<0.001) and between ADMA and systolic blood pressure (p=0.005) and pulse pressure (p=0.003) were shown. Conclusions: Homoarginine and ADMA levels are decreased and associated with cardiovascular risk factors in children with T1D without being affected by atorvastatin
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