613 research outputs found
High temperature magnetic stabilization of cobalt nanoparticles by an antiferromagnetic proximity effect
Thermal activation tends to destroy the magnetic stability of small magnetic
nanoparticles, with crucial implications in ultra-high density recording among
other applications. Here we demonstrate that low blocking temperature
ferromagnetic (FM) Co nanoparticles (TB<70 K) become magnetically stable above
400 K when embedded in a high N\'eel temperature antiferromagnetic (AFM) NiO
matrix. The origin of this remarkable TB enhancement is due to a magnetic
proximity effect between a thin CoO shell (with low N\'eel temperature, TN; and
high anisotropy, KAFM) surrounding the Co nanoparticles and the NiO matrix
(with high TN but low KAFM). This proximity effect yields an effective AFM with
an apparent TN beyond that of bulk CoO, and an enhanced anisotropy compared to
NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations
via core-shell exchange-bias coupling, leading to the observed TB increase.
Mean-field calculations provide a semi-quantitative understanding of this
magnetic- proximity stabilization mechanism
Monitoring stimulated emission at the single photon level in one-dimensional atoms
We theoretically investigate signatures of stimulated emission at the single
photon level for a two-level atom interacting with a one-dimensional light
field. We consider the transient regime where the atom is initially excited,
and the steady state regime where the atom is continuously driven with an
external pump. The influence of pure dephasing is studied, clearly showing that
these effects can be evidenced with state of the art solid state devices. We
finally propose a scheme to demonstrate the stimulation of one optical
transition by monitoring another one, in three-level one-dimensional atoms.Comment: 4 pages, 4 figures. Improved introduction; Comments adde
High-resolution spatial mapping of a superconducting NbN wire using single-electron detection
Superconducting NbN wires have recently received attention as detectors for
visible and infrared photons. We present experiments in which we use a NbN wire
for high-efficiency (40 %) detection of single electrons with keV energy. We
use the beam of a scanning electron microscope as a focussed, stable, and
calibrated electron source. Scanning the beam over the surface of the wire
provides a map of the detection efficiency. This map shows features as small as
150 nm, revealing wire inhomogeneities. The intrinsic resolution of this
mapping method, superior to optical methods, provides the basis of a
characterization tool relevant for photon detectors.Comment: 2009 IEEE Toronto International Conference, Science and Technology
for Humanity (TIC-STH
Exploiting the quantum Zeno effect to beat photon loss in linear optical quantum information processors
We devise a new technique to enhance transmission of quantum information
through linear optical quantum information processors. The idea is based on
applying the Quantum Zeno effect to the process of photon absorption. By
frequently monitoring the presence of the photon through a QND (quantum
non-demolition) measurement the absorption is suppressed. Quantum information
is encoded in the polarization degrees of freedom and is therefore not affected
by the measurement. Some implementations of the QND measurement are proposed.Comment: 4 pages, 1 figur
Generating and probing a two-photon Fock state with a single atom in a cavity
A two-photon Fock state is prepared in a cavity sustaining a "source mode "
and a "target mode", with a single circular Rydberg atom. In a third-order
Raman process, the atom emits a photon in the target while scattering one
photon from the source into the target. The final two-photon state is probed by
measuring by Ramsey interferometry the cavity light shifts induced by the
target field on the same atom. Extensions to other multi-photon processes and
to a new type of micromaser are briefly discussed
Plasmonic nickel nanoantennas
7 pĂĄginas, 6 figuras.-- El pdf del artĂculo es la versiĂłn post-print.-- et al.The fundamental optical properties of pure nickel nanostructures are studied by far-field extinction spectroscopy and optical near-field microscopy, providing direct experimental evidence of the existence of particle plasmon resonances predicted by theory. Experimental and calculated near-field maps allow for unambiguous identification of dipolar plasmon modes. By comparing calculated near-field and far-field spectra, dramatic shifts are found between the near-field and far-field plasmon resonances, which are much stronger than in gold nanoantennas. Based on a simple damped harmonic oscillator model to describe plasmonic resonances, it is possible to explain these shifts as due to plasmon damping.Supported by the European FP7 project âNanoantennaâ (FP7-HEALTH-F5-2009-241818-NANOANTENNA) and the National Project MAT2009 â08398 from the Spanish Ministerio de Ciencia
e Innovacion. J.A. acknowledges fi nancial help by the Department of Industry of the Basque Government through the ETORTEK program NANOPHOT. P.V. acknowledges funding from the Basque Government under Programs No. PI2009â17 as well as the Spanish Ministry of Science and Education under Project No. MAT2009â07980. Z. P. acknowledges support from Swedish Foundation for
Strategic Research through RMA08â0109 âFunctional Electromagnetic Metamaterialsâ program. J. N. acknowledges funding from the Generalitat de Catalunya and the Spanish Ministry of Science
and Education through No. 2009-SGR-1292 and No. MAT2010â20616-C02 projects. A.D. acknowledges support from the Swedish Research Council.Peer reviewe
Trapping of single atoms in cavity QED
By integrating the techniques of laser cooling and trapping with those of
cavity quantum electrodynamics (QED), single Cesium atoms have been trapped
within the mode of a small, high finesse optical cavity in a regime of strong
coupling. The observed lifetime for individual atoms trapped within the cavity
mode is ms, and is limited by fluctuations of light forces
arising from the far-detuned intracavity field. This initial realization of
trapped atoms in cavity QED should enable diverse protocols in quantum
information science.Comment: 4 pages, 4 figure
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