1,754 research outputs found
An interleaved sampling scheme for the characterization of single qubit dynamics
In this paper, we demonstrate that interleaved sampling techniques can be
used to characterize the Hamiltonian of a qubit and its environmental
decoherence rate. The technique offers a significant advantage in terms of the
number of measurements that are required to characterize a qubit. When compared
to the standard Nyquist-Shannon sampling rate, the saving in the total
measurement time for the interleaved method is approximately proportional to
the ratio of the sample rates.Comment: 9 pages, 4 figure
An algorithm for simulating the Ising model on a type-II quantum computer
Presented here is an algorithm for a type-II quantum computer which simulates
the Ising model in one and two dimensions. It is equivalent to the Metropolis
Monte-Carlo method and takes advantage of quantum superposition for random
number generation. This algorithm does not require the ensemble of states to be
measured at the end of each iteration, as is required for other type-II
algorithms. Only the binary result is measured at each node which means this
algorithm could be implemented using a range of different quantum computing
architectures. The Ising model provides an example of how cellular automata
rules can be formulated to be run on a type-II quantum computer.Comment: 14 pages, 11 figures. Accepted for publication in Computer Physics
Communication
Minimal Steiner Trees for 2kĂ—2kSquare Lattices
AbstractWe prove a conjecture of Chung, Graham, and Gardner (Math. Mag.62(1989), 83–96), giving the form of the minimal Steiner trees for the set of points comprising the vertices of a 2k×2ksquare lattice. Each full component of these minimal trees is the minimal Steiner tree for the four vertices of a square
Dynamical control of correlated states in a square quantum dot
In the limit of low particle density, electrons confined to a quantum dot
form strongly correlated states termed Wigner molecules, in which the Coulomb
interaction causes the electrons to become highly localized in space. By using
an effective model of Hubbard-type to describe these states, we investigate how
an oscillatory electric field can drive the dynamics of a two-electron Wigner
molecule held in a square quantum dot. We find that, for certain combinations
of frequency and strength of the applied field, the tunneling between various
charge configurations can be strongly quenched, and we relate this phenomenon
to the presence of anti-crossings in the Floquet quasi-energy spectrum. We
further obtain simple analytic expressions for the location of these
anti-crossings, which allows the effective parameters for a given quantum dot
to be directly measured in experiment, and suggests the exciting possibility of
using ac-fields to control the time evolution of entangled states in mesoscopic
devices.Comment: Replaced with version to be published in Phys. Rev.
Classtalk: A Classroom Communication System for Active Learning
This pdf file is an article describing the advantages of using Classtalk technology in the classroom to enhance classroom communication. Classtalk technology cab facilitate the presentation of questions for small group work, collec the student answers and then display histograms showing how the class answered. This new communication technology can help instructors create a more interactive, student centered classroom, especially when teaching large courses. The article describes Classtalk as a very useful tool not only for engaging students in active learning, but also for enhancing the overall communication within the classroom. This article is a selection from the electronic Journal for Computing in Higher Education. Educational levels: Graduate or professional
Strong-field terahertz-optical mixing in excitons
Driving a double-quantum-well excitonic intersubband resonance with a
terahertz (THz) electric field of frequency \omega_{THz} generated terahertz
optical sidebands \omega=\omega_{THz}+\omega_{NIR} on a weak NIR probe. At high
THz intensities, the intersubband dipole energy which coupled two excitons was
comparable to the THz photon energy. In this strong-field regime the sideband
intensity displayed a non-monotonic dependence on the THz field strength. The
oscillating refractive index which gives rise to the sidebands may be
understood by the formation of Floquet states, which oscillate with the same
periodicity as the driving THz field.Comment: 4 pages, 6 figure
Blackbody Radiation and the Scaling Symmetry of Relativistic Classical Electron Theory with Classical Electromagnetic Zero-Point Radiation
It is pointed out that relativistic classical electron theory with classical
electromagnetic zero-point radiation has a scaling symmetry which is suitable
for understanding the equilibrium behavior of classical thermal radiation at a
spectrum other than the Rayleigh-Jeans spectrum. In relativistic classical
electron theory, the masses of the particles are the only scale-giving
parameters associated with mechanics while the action-angle variables are scale
invariant. The theory thus separates the interaction of the action variables of
matter and radiation from the scale-giving parameters. Classical zero-point
radiation is invariant under scattering by the charged particles of
relativistic classical electron theory. The basic ideas of the matter
-radiation interaction are illustrated in a simple relativistic classical
electromagnetic example.Comment: 18 page
Strangeness Enhancement in p-A Collisions: Consequences for the Interpretation of Strangeness Production in A-A Collisions
Published measurements of semi-inclusive Lambda production in p-Au collisions
at the AGS are used to estimate the yields of singly strange hadrons in
nucleus-nucleus A-A collisions. Results of a described extrapolation technique
are shown and compared to measurements of K+ production in Si-Al, Si-Au, and
Au-Au collisions at the AGS and net Lambda production in Su-Su, S-Ag, Pb-Pb,
and inclusive p-A collisions at the SPS. The extrapolations can account for
more than 75% of the measured strange particle yields in all of the studied
systems except for very central Au-Au collisions at the AGS where RQMD
comparisons suggest large re-scattering contributions.Comment: 9 pages, 4 figure
The structure of oppositionality: Response disposition and situational aspects
Background: The Amsterdam Scale of Oppositionality (ASO) is a recently developed self-report instrument to measure the full range of oppositionality. It was used to test the assumption that oppositionality can best be conceptualized as a combination of emotions and behaviors varying across contexts, i.e., with parents, peers and authority figures. Method: The sample consisted of 560 boys and 598 girls, aged 8 to 12 years. The thirty items of the ASO, grouped in item parcels, were analyzed using confirmatory factor analyses. Results: Results confirmed the main hypothesis. The best fitting models contained strongly related emotional and behavioral factors and three mutually related situational factors. Oppositionality appeared to be to a large extent situation-specific. Girls are more affected by the situation than boys and show less oppositionality only outside the family context. Conclusions: Results are discussed with respect to the concept of oppositionality, varying expectations for interpersonal consequences, and implications for clinical assessment and studies of inter-informant reliability
Body mass index, but not FTO genotype or major depressive disorder, influences brain structure
Obesity and major depressive disorder (MDD) are highly prevalent and often comorbid health conditions. Both are associated with differences in brain structure and are genetically influenced. Yet, little is known about how obesity, MDD, and known risk genotypes might interact in the brain. Subjects were 81 patients with MDD (mean age 48.6 years) and 69 matched healthy controls (mean age 51.2 years). Subjects underwent 1.5T magnetic resonance imaging, genotyping for the fat mass and obesity associated (FTO) gene rs3751812 polymorphism, and measurements for body mass index (BMI). We conducted a whole brain voxelwise analysis using tensor-based morphometry (TBM) to examine the main and interaction effects of diagnosis, BMI and FTO genotype. Significant effects of BMI were observed across widespread brain regions, indicating reductions in predominantly subcortical and white matter areas associated with increased BMI, but there was no influence of MDD or FTO rs3751812 genotype. There were no significant interaction effects. Within MDD patients, there was no effect of current depressive symptoms; however the use of antidepressant medication was associated with reductions in brain volume in the frontal lobe and cerebellum. Obesity affects brain structure in both healthy participants and MDD patients; this influence may account for some of the brain changes previously associated with MDD. BMI and the use of medication should ideally be measured and controlled for when conducting structural brain imaging research in MDD
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