1,834 research outputs found
Localized magnetoplasmon modes arising from broken translational symmetry in semiconductor superlattices
The electromagnetic propagator associated with the localized collective
magnetoplasmon excitations in a semiconductor superlattice with broken
translational symmetry, is calculated analytically within linear response
theory. We discuss the properties of these collective excitations in both
radiative and non-radiative regimes of the electromagnetic spectra. We find
that low frequency retarded modes arise when the surface density of carriers at
the symmetry breaking layer is lower than the density at the remaining layers.
Otherwise a doublet of localized, high-frequency magnetoplasmon-like modes
occurs.Comment: Revtex file + separate pdf figure
CP violation in the decay mode
Within the framework of Standard Model, the exclusive decay mode is studied. Although the usual short distance contribution is
small compared to the similar mode, the process offers the
possibility of studying the CP violation, a feature absent in the
counterpart.Comment: 11 page latex file including 2 ps figures. Typos corrected, minor
changes. To appear in PR
Radiative corrections and quantum gates in molecular systems
We propose a method for quantum information processing using molecules
coupled to an external laser field. This utilizes molecular interactions,
control of the external field and an effective energy shift of the
doubly-excited state of two coupled molecules. Such a level shift has been seen
in the two-photon resonance experiments recently reported in Ref. [1]. Here we
show that this can be explained in terms of the QED Lamb shift. We quantify the
performance of the proposed quantum logic gates in the presence of dissipative
mechanisms. The unitary transformations required for performing one- and
two-qubit operations can be implemented with present day technology.Comment: 4 pages, 3 figures, Updated to correct important missing referenc
Vitamin A Status of Women and Children in Yaoundé and Douala, Cameroon, is Unchanged One Year after Initiation of a National Vitamin A Oil Fortification Program.
Vitamin A (VA) fortification of cooking oil is considered a cost-effective strategy for increasing VA status, but few large-scale programs have been evaluated. We conducted representative surveys in Yaoundé and Douala, Cameroon, 2 years before and 1 year after the introduction of a mandatory national program to fortify cooking oil with VA. In each survey, 10 different households were selected within each of the same 30 clusters (n = ~300). Malaria infection and plasma indicators of inflammation and VA (retinol-binding protein, pRBP) status were assessed among women aged 15-49 years and children aged 12-59 months, and casual breast milk samples were collected for VA and fat measurements. Refined oil intake was measured by a food frequency questionnaire, and VA was measured in household oil samples post-fortification. Pre-fortification, low inflammation-adjusted pRBP was common among children (33% <0.83 µmol/L), but not women (2% <0.78 µmol/L). Refined cooking oil was consumed by >80% of participants in the past week. Post-fortification, only 44% of oil samples were fortified, but fortified samples contained VA concentrations close to the target values. Controlling for age, inflammation, and other covariates, there was no difference in the mean pRBP, mean breast milk VA, prevalence of low pRBP, or prevalence of low milk VA between the pre- and post-fortification surveys. The frequency of refined oil intake was not associated with VA status indicators post-fortification. In sum, after a year of cooking oil fortification with VA, we did not detect evidence of increased plasma RBP or milk VA among urban women and preschool children, possibly because less than half of the refined oil was fortified. The enforcement of norms should be strengthened, and the program should be evaluated in other regions where the prevalence of VA deficiency was greater pre-fortification
On the use of dielectric elements in axion searches with microwave resonant cavities
This study explores the primary effects of dielectric materials in a resonant
cavity-based search for axion dark matter. While dielectrics prove beneficial
in numerous cases, their incorporation may lead to less-than-optimal
performance, especially for the lowest TM mode. Additionally, the stronger
confinement of the electric field inside the dielectrics can exacerbate mode
mixings, in particular for higher-order modes. Case studies have been carried
out using a combination of analytical solutions and numerical simulations. The
findings indicate dielectric cavities employing the mode
experience a significant reduction in sensitivity when compared to a similar
search conducted in a cavity at equivalent frequency using no dielectrics.Comment: 10 pages, 7 figure
Decoherence of quantum registers
The dynamical evolution of a quantum register of arbitrary length coupled to
an environment of arbitrary coherence length is predicted within a relevant
model of decoherence. The results are reported for quantum bits (qubits)
coupling individually to different environments (`independent decoherence') and
qubits interacting collectively with the same reservoir (`collective
decoherence'). In both cases, explicit decoherence functions are derived for
any number of qubits. The decay of the coherences of the register is shown to
strongly depend on the input states: we show that this sensitivity is a
characteristic of types of coupling (collective and independent) and not
only of the collective coupling, as has been reported previously. A non-trivial
behaviour ("recoherence") is found in the decay of the off-diagonal elements of
the reduced density matrix in the specific situation of independent
decoherence. Our results lead to the identification of decoherence-free states
in the collective decoherence limit. These states belong to subspaces of the
system's Hilbert space that do not get entangled with the environment, making
them ideal elements for the engineering of ``noiseless'' quantum codes. We also
discuss the relations between decoherence of the quantum register and
computational complexity based on the new dynamical results obtained for the
register density matrix.Comment: Typos corrected. Discussion and references added. 1 figure + 3 tables
added. This updated version contains 13 (double column) pages + 8 figures.
PRA in pres
Exciton entanglement in two coupled semiconductor microcrystallites
Entanglement of the excitonic states in the system of two coupled
semiconductor microcrystallites, whose sizes are much larger than the Bohr
radius of exciton in bulk semiconductor but smaller than the relevant optical
wavelength, is quantified in terms of the entropy of entanglement. It is
observed that the nonlinear interaction between excitons increases the maximum
values of the entropy of the entanglement more than that of the linear coupling
model. Therefore, a system of two coupled microcrystallites can be used as a
good source of entanglement with fixed exciton number. The relationship between
the entropy of the entanglement and the population imbalance of two
microcrystallites is numerically shown and the uppermost envelope function for
them is estimated by applying the Jaynes principle.Comment: 16 pages, 6 figure
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