1,317 research outputs found
High temperature thermal conductivity of 2-leg spin-1/2 ladders
Based on numerical simulations, a study of the high temperature, finite
frequency, thermal conductivity of spin-1/2 ladders is
presented. The exact diagonalization and a novel Lanczos technique are
employed.The conductivity spectra, analyzed as a function of rung coupling,
point to a non-diverging limit but to an unconventional low frequency
behavior. The results are discussed with perspective recent experiments
indicating a significant magnetic contribution to the energy transport in
quasi-one dimensional compounds.Comment: 4 pages, 4 figure
Photoluminescence and spectral switching of single CdSe/ZnS colloidal nanocrystals in poly(methyl methacrylate)
Emission from single CdSe nanocrystals in PMMA was investigated. A fraction
of the nanocrystals exhibiting switching between two energy states, which have
similar total intensities, but distinctly different spectra were observed. We
found that the spectral shift characteristic frequency increases with the pump
power. By using the dynamic shift in the spectral position of emission peaks,
we were able to correlate peaks from the same nanocrystal. The measured
correlation is consistent with assignment of low energy lines to phonon
replicas.Comment: 5 pages, 4 figure
Indirect coupling between spins in semiconductor quantum dots
The optically induced indirect exchange interaction between spins in two
quantum dots is investigated theoretically. We present a microscopic
formulation of the interaction between the localized spin and the itinerant
carriers including the effects of correlation, using a set of canonical
transformations. Correlation effects are found to be of comparable magnitude as
the direct exchange. We give quantitative results for realistic quantum dot
geometries and find the largest couplings for one dimensional systems.Comment: 4 pages, 3 figure
Optical RKKY Interaction between Charged Semiconductor Quantum Dots
We show how a spin interaction between electrons localized in neighboring
quantum dots can be induced and controlled optically. The coupling is generated
via virtual excitation of delocalized excitons and provides an efficient
coherent control of the spins. This quantum manipulation can be realized in the
adiabatic limit and is robust against decoherence by spontaneous emission.
Applications to the realization of quantum gates, scalable quantum computers,
and to the control of magnetization in an array of charged dots are proposed.Comment: 4 pages, 2 figure
Optically-controlled single-qubit rotations in self-assembled InAs quantum dots
We present a theory of the optical control of the spin of an electron in an
InAs quantum dot. We show how two Raman-detuned laser pulses can be used to
obtain arbitrary single-qubit rotations via the excitation of an intermediate
trion state. Our theory takes into account a finite in-plane hole -factor
and hole-mixing. We show that such rotations can be performed to high
fidelities with pulses lasting a few tens of picoseconds.Comment: 6 pages, 4 figures; minor changes, J-ref adde
Associations between diurnal preference, sleep quality and externalizing behaviours: a behavioural genetic analysis
Background - Certain aspects of sleep co-occur with externalizing behaviours in youth, yet little is known about these associations in adults. The present study: (1) examines the associations between diurnal preference (morningness versus eveningness), sleep quality and externalizing behaviours; (2) explores the extent to which genetic and environmental influences are shared between or are unique to these phenotypes; (3) examines the extent to which genetic and environmental influences account for these associations.
Method - Questionnaires assessing diurnal preference, sleep quality and externalizing behaviours were completed by 1556 young adult twins and siblings.
Results - A preference for eveningness and poor sleep quality were associated with greater externalizing symptoms [r=0.28 (95% CI 0.23–0.33) and 0.34 (95% CI 0.28–0.39), respectively]. A total of 18% of the genetic influences on externalizing behaviours were shared with diurnal preference and sleep quality and an additional 14% were shared with sleep quality alone. Non-shared environmental influences common to the phenotypes were small (2%). The association between diurnal preference and externalizing behaviours was mostly explained by genetic influences [additive genetic influence (A)=80% (95% CI 0.56–1.01)], as was the association between sleep quality and externalizing behaviours [A=81% (95% CI 0.62–0.99)]. Non-shared environmental (E) influences accounted for the remaining variance for both associations [E=20% (95% CI −0.01 to 0.44) and 19% (95% CI 0.01–0.38), respectively].
Conclusions - A preference for eveningness and poor sleep quality are moderately associated with externalizing behaviours in young adults. There is a moderate amount of shared genetic influences between the phenotypes and genetic influences account for a large proportion of the association between sleep and externalizing behaviours. Further research could focus on identifying specific genetic polymorphisms common to both sleep and externalizing behaviours
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