2,775 research outputs found
Storing images in warm atomic vapor
Reversible and coherent storage of light in atomic medium is a key-stone of
future quantum information applications. In this work, arbitrary
two-dimensional images are slowed and stored in warm atomic vapor for up to 30
s, utilizing electromagnetically induced transparency. Both the intensity
and the phase patterns of the optical field are maintained. The main limitation
on the storage resolution and duration is found to be the diffusion of atoms. A
techniqueanalogous to phase-shift lithography is employed to diminish the
effect of diffusion on the visibility of the reconstructed image
Measurement of Dicke Narrowing in Electromagnetically Induced Transparency
Dicke narrowing is a phenomena that dramatically reduces the Doppler width of
spectral lines, due to frequent velocity-changing collisions. A similar
phenomena occurs for electromagnetically induced transparency (EIT) resonances,
and facilitates ultra-narrow spectral features in room-temperature vapor. We
directly measure the Dicke-like narrowing by studying EIT line-shapes as a
function of the angle between the pump and the probe beams. The measurements
are in good agreement with an analytic theory with no fit parameters. The
results show that Dicke narrowing can increase substantially the tolerance of
hot-vapor EIT to angular deviations. We demonstrate the importance of this
effect for applications such as imaging and spatial solitons using a
single-shot imaging experiment, and discuss the implications on the feasibility
of storing images in atomic vapor.Comment: Introduction revise
Topological stability of stored optical vortices
We report an experiment in which an optical vortex is stored in a vapor of Rb
atoms. Due to its 2\pi phase twist, this mode, also known as the Laguerre-Gauss
mode, is topologically stable and cannot unwind even under conditions of strong
diffusion. To supplement our finding, we stored a flat phase Gaussian beam with
a dark center. Contrary to the optical vortex, which stays stable for over 100
microseconds, the dark center in the retrieved flat-phased image was filled
with light at storage times as small as 10 microseconds. This experiment proves
that higher electromagnetic modes can be converted into atomic coherences, and
that modes with phase singularities are robust to decoherence effects such as
diffusion. This opens the possibility to more elaborate schemes for two
dimensional information storage in atomic vapors.Comment: 4 pages, 4 figures v2: minor grammatical corrections v3: problem with
references fixed v4: minor clarifications added to the tex
Improving Access and Quality in Early Childhood Development Programs: Experimental Evidence from The Gambia
We evaluate two experiments of early childhood development (ECD) programs in The Gambia: one increasing access to services, and another improving service quality. In the first experiment, new community-based ECD centers were introduced to randomly chosen villages that had no pre-existing structured ECD services. In the second experiment, a randomly assigned subset of existing ECD centers received intensive provider training. We find no evidence that either intervention improved average levels of child development. Exploratory analysis suggests that the first experiment, which increased access to community-based ECD services, led to declines in child development among children from less disadvantaged households
Radiation tolerance studies of silicon microstrip sensors for the CBM Silicon Tracking System
Double-sided silicon microstrip sensors will be used in the Silicon Tracking System of the CBM experiment. During experimental run they will be exposed to a radiation field of up to 1x1014 1 MeV neq cm-2. Radiation tolerance studies were made on prototypes from two different vendors. Results from these prototype detectors before and after irradiation to twice that neutron fluence are discussed
Bose-Fermi mixtures in 1D optical superlattices
The zero temperature phase diagram of binary boson-fermion mixtures in
two-colour superlattices is investigated. The eigenvalue problem associated
with the Bose-Fermi-Hubbard Hamiltonian is solved using an exact numerical
diagonalization technique, supplemented by an adaptive basis truncation scheme.
The physically motivated basis truncation allows to access larger systems in a
fully controlled and very flexible framework. Several experimentally relevant
observables, such as the matter-wave interference pattern and the
condensatefraction, are investigated in order to explore the rich phase
diagram. At symmetric half filling a phase similar to the Mott-insulating phase
in a commensurate purely bosonic system is identified and an analogy to recent
experiments is pointed out. Furthermore a phase of complete localization of the
bosonic species generated by the repulsive boson-fermion interaction is
identified. These localized condensates are of a different nature than the
genuine Bose-Einstein condensates in optical lattices.Comment: 18 pages, 9 figure
Spectral density asymptotics for Gaussian and Laguerre -ensembles in the exponentially small region
The first two terms in the large asymptotic expansion of the
moment of the characteristic polynomial for the Gaussian and Laguerre
-ensembles are calculated. This is used to compute the asymptotic
expansion of the spectral density in these ensembles, in the exponentially
small region outside the leading support, up to terms . The leading form
of the right tail of the distribution of the largest eigenvalue is given by the
density in this regime. It is demonstrated that there is a scaling from this,
to the right tail asymptotics for the distribution of the largest eigenvalue at
the soft edge.Comment: 19 page
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