17,861 research outputs found
One-dimensional description of a Bose-Einstein condensate in a rotating closed-loop waveguide
We propose a general procedure for reducing the three-dimensional Schrodinger
equation for atoms moving along a strongly confining atomic waveguide to an
effective one-dimensional equation. This procedure is applied to the case of a
rotating closed-loop waveguide. The possibility of including mean-field atomic
interactions is presented. Application of the general theory to characterize a
new concept of atomic waveguide based on optical tweezers is finally discussed
All-Optical Depletion of Dark Excitons from a Semiconductor Quantum Dot
Semiconductor quantum dots are considered to be the leading venue for
fabricating on-demand sources of single photons. However, the generation of
long-lived dark excitons imposes significant limits on the efficiency of these
sources. We demonstrate a technique that optically pumps the dark exciton
population and converts it to a bright exciton population, using intermediate
excited biexciton states. We show experimentally that our method considerably
reduces the DE population while doubling the triggered bright exciton emission,
approaching thereby near-unit fidelity of quantum dot depletion.Comment: 5 pages, 3 figure
Effect of trap symmetry and atom-atom interactions on a trapped atom interferometer with internal state labelling
In this paper, we study the dynamics of a trapped atom interferometer with
internal state labelling in the presence of interactions. We consider two
situations: an atomic clock in which the internal states remain superposed, and
an inertial sensor configuration in which they are separated. From the average
spin evolution, we deduce the fringe contrast and the phase-shift. In the clock
configuration, we recover the well-known identical spin rotation effect (ISRE)
which can significantly increase the spin coherence time. We also find that the
magnitude of the effect depends on the trap geometry in a way that is
consistent with our recent experimental results in a clock configuration [M.
Dupont-Nivet, and al., New J. Phys., 20, 043051 (2018)], where ISRE was not
observed. In the case of an inertial sensor, we show that despite the spatial
separation it is still possible to increase the coherence time by using mean
field interactions to counteract asymmetries of the trapping potential.Comment: 18 pages, 5 figure
Espécies arbóreas da sede da Embrapa Amazônia Oriental: conservação ex situ e um novo espaço de educação ambiental em Belém.
Publicado também on-line
Modeling urban street patterns
Urban streets patterns form planar networks whose empirical properties cannot
be accounted for by simple models such as regular grids or Voronoi
tesselations. Striking statistical regularities across different cities have
been recently empirically found, suggesting that a general and
details-independent mechanism may be in action. We propose a simple model based
on a local optimization process combined with ideas previously proposed in
studies of leaf pattern formation. The statistical properties of this model are
in good agreement with the observed empirical patterns. Our results thus
suggests that in the absence of a global design strategy, the evolution of many
different transportation networks indeed follow a simple universal mechanism.Comment: 4 pages, 5 figures, final version published in PR
Local formation of nitrogen-vacancy centers in diamond by swift heavy ions
We exposed nitrogen-implanted diamonds to beams of swift uranium and gold
ions (~1 GeV) and find that these irradiations lead directly to the formation
of nitrogen vacancy (NV) centers, without thermal annealing. We compare the
photoluminescence intensities of swift heavy ion activated NV- centers to those
formed by irradiation with low-energy electrons and by thermal annealing. NV-
yields from irradiations with swift heavy ions are 0.1 of yields from low
energy electrons and 0.02 of yields from thermal annealing. We discuss possible
mechanisms of NV-center formation by swift heavy ions such as electronic
excitations and thermal spikes. While forming NV centers with low efficiency,
swift heavy ions enable the formation of three dimensional NV- assemblies over
relatively large distances of tens of micrometers. Further, our results show
that NV-center formation is a local probe of (partial) lattice damage
relaxation induced by electronic excitations from swift heavy ions in diamond.Comment: to be published in Journal of Applied Physic
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